Characters of Halo

Steve Downes and Jen Taylor, the voices of Master Chief and Cortana, at HaloFest during PAX Prime 2011

The Halo series features voice work by television and film actors including Ron Perlman, Orlando Jones, Michelle Rodriguez, Robert Davi, and Terence Stamp.[9] Voice acting became more important as Halo: Combat Evolved's sequels were developed; Halo 2 had 2,000 lines of combat dialogue, while Halo 3 has in excess of 14,000 lines.[10] Some actors voiced their lines in remote locations, while others traveled to a studio to record their lines.[11] In interviews, Halo's voice actors stated that they had no idea that the games would become such a critical and commercial success. Steve Downes, the voice of the game's protagonist, stated that generally when a voice actor has finished their lines, their involvement with the game ends. As the characters in Combat Evolved were relatively undefined, the voice actors were given leeway to develop their own style and personality.[11]

Aside from major character roles, members of the Halo community and Halo fans have had small roles in the games. The cast from the machinima Red vs. Blue won a lengthy charity auction for a voice role in Halo 3, and do a comedy routine which changes depending on the difficulty level the game is played on.[12] Cast members of the defunct TV show Firefly—Alan Tudyk, Nathan Fillion, and Adam Baldwin—have roles as marines in Halo 3[9] as well as Halo 3: ODST[13][14] and Halo 5: Guardians.

List indicator(s)

• This table shows the recurring characters and the actors who have portrayed them throughout the franchise.
• A dark grey cell indicates the character was not in the film, or that the character's presence in the film has not yet been announced.
• A ^Y indicates an appearance as a younger version of a pre-existing character.
• A ^C indicates a cameo appearance.
• A ^V indicates a voice role only.
• A ^P indicates an appearance in onscreen photographs only.
• A ^D indicates an appearance in deleted scenes only.
• A ^U indicates an uncredited role.
• A ^M indicates a motion-capture role.

Master Chief Petty Officer John-117, commonly referred to as simply the Master Chief, is the main protagonist and main playable character in many of the Halo games. The character is voiced by Steve Downes, a Chicago disc jockey. One of the last SPARTAN-II supersoldiers still in active service, the Master Chief inspires awe and fear in the alien Covenant, who refer to him as a "demon".[15] Assisted by the artificial intelligence Cortana, he prevents the catastrophic firing of Installation 04 in Halo: Combat Evolved. Bungie staff member Joseph Staten noted that until the Master Chief was created, Bungie had not paid any attention to how to make people want to play in the world of Halo. "Master Chief is really what kicked off the creativity," he said, "in terms of how people react to him. He's a space marine in really cool green armor."[16] The character has since become a gaming icon, the mascot of the Xbox, and was rated as one of the greatest videogame characters of all time by Electronic Gaming Monthly.[17]

Cortana, voiced in the games by Jen Taylor, is the artificial intelligence (AI) who assists the Master Chief in the video games. She is one of many "smart" AIs, and is based on the brain of Dr. Halsey; the nature of her programming means that she will eventually "think" herself to death after a lifespan of about seven years. In Halo 4, Cortana begins to succumb to her age, and sacrifices herself to save Chief and Earth from the Forerunner Didact, but in Halo 5: Guardians, it is revealed that she had survived the ordeal. Having found access to the Domain, a Forerunner repository of knowledge, Cortana believes that AIs should serve as the galaxy's caretakers, putting her in conflict with her creators. Cortana was named the fifth best supporting character,[18] and one of the "50 Greatest Female Characters"[19] in a video game. Reviewers noted the character's determination and fearlessness meshed perfectly with the Master Chief,[19] and that Cortana provides an anchor linking players to Halo's story.[20]

Avery Junior Johnson is a Marine sergeant major who leads human forces against alien assaults throughout the Halo series. The character is voiced by David Scully. Johnson and a few other Marines survive the destruction of Installation 04 and are rescued by Cortana and the Master Chief during the novel Halo: First Strike. Johnson plays a much larger role in Halo 2, joining forces with the Arbiter to stop Tartarus from activating Installation 05.[21] In Halo 2, he is awarded the Colonial Cross for his heroic actions at Installation 04,[22] In Halo 3, the Forerunner construct 343 Guilty Spark kills him when Johnson tries to activate the incomplete Halo at the Ark. Johnson is featured in The Halo Graphic Novel story, "Breaking Quarantine," which details Johnson's escape from the Flood in Halo: Combat Evolved, and a main character in the 2007 novel Halo: Contact Harvest. Johnson later appears as a main character in Halo: Silent Storm where it's revealed that he's a Spartan-I, a precursor to the Spartan-II program that the Master Chief is a part of. Taking place about a year after Contact Harvest, Johnson is recruited to be a part of a strike force launching a counterattack behind enemy lines to buy humanity some time. Johnson is recruited both for his experience with the Covenant and his Spartan training and acts as a mentor and friend to the young Master Chief, becoming one of the few people the Spartans trust implicitly on the mission where insurrectionists are trying to destroy them and they can't be sure of whom to trust.

In many ways similar to the stereotype of charismatic black Marines found in other science fiction (such as Sergeant Apone in Aliens whom Johnson was partially based on),[23] some publications found Johnson, though enjoyable, somewhat of a flat character. In an interview for Halo: Contact Harvest, Joseph Staten of Bungie admitted that Johnson was a static character in Halo: Combat Evolved, and that despite the character's potential, "he sort of inherited those caricature aspects [from Halo]."[23] Contact Harvest was a chance "to do right by Johnson, to give him the rich, fully fleshed out back-story he deserves, that we have never been able to give him in the game."[23]

Captain Jacob Keyes (voiced by Pete Stacker) is a captain in the UNSC who appears in Halo: Reach, Halo: Combat Evolved, its novelization, Halo: The Flood, Halo: The Cole Protocol, and Halo: The Fall of Reach. His first chronological appearance is in The Fall of Reach, where, as a young Lieutenant, he accompanies Dr. Catherine Halsey on her mission to screen possible SPARTAN-II Project subjects.[24] In 2534, Lieutenant Keyes plays a pivotal role in saving a million insurrectionists' lives from Covenant forces.[25] By 2552, midway through The Fall of Reach Keyes is commander of the Iroquois, a UNSC destroyer.[26] Keyes is promoted to Captain after he singlehandedly defeats four Covenant ships about to attack a human colony by performing a maneuver later named the "Keyes Loop."[27] When the Iroquois is recalled to the human bastion Reach, a Covenant tracking device aboard the ship alerts the Covenant to the planet's existence, and they proceed to attack the colony. As the planet is glassed by the Covenant, Keyes follows Cole Protocol, which leads his new ship, the Pillar of Autumn to Halo. There, Keyes leads a guerrilla insurgency against the Covenant, until he is captured and assimilated by the parasitic Flood. After being found by the Master Chief in his assimilated state, the Master Chief sadly ends Keyes' suffering by punching into his skull to retrieve Keyes' neural implants in order to destroy the Pillar of Autumn. His daughter is Miranda Keyes.

Commander Miranda Keyes is the daughter of Jacob Keyes and Catherine Halsey, whom she lived with in her younger years. Halsey and Miranda had a falling out in which she changed her last name (then Halsey) to her father's name (Keyes). Miranda appears in Halo 2, Halo 3 and in the final chapter of Halo: The Cole Protocol. At the beginning of Halo 2, Keyes is present at an awards ceremony on board the Cairo defense platform above Earth to accept a medal posthumously for her father. Soon after, a Covenant fleet launches an attack on Earth, and Keyes takes control of the UNSC ship In Amber Clad and assists in the defense of New Mombasa, Kenya. When the Prophet of Regret retreats from Earth, Keyes orders In Amber Clad to follow; this results in the discovery of Installation 05, another Halo. Keyes, along with Johnson and a squad of Marines, head for Halo's library in order to retrieve the Activation Index and prevent the ring's activation while the Master Chief assassinates the Prophet of Regret; in the process, she and Johnson are captured by the Brute Chieftain Tartarus. As a "Reclaimer," only she or another human can insert the Index into Halo's control panel, and Tartarus attempts to make her do this. When the Arbiter tries to stop the firing, Tartarus forces Keyes to insert the Index, initiating Halo's firing sequence. After the Arbiter engages and kills Tartarus, Keyes successfully removes the Index and prevents Halo from activating, but inadvertently causes all the remaining Halo installations to enter standby mode, enabling the remote firing of these installations from The Ark.[28] In Halo 3, Miranda Keyes returns to Earth and leads the pursuit of the Prophet of Truth through the portal he creates using the artifact buried under New Mombasa, which leads to the Ark. When Sergeant Johnson is captured by the Covenant to activate the installation, she attempts to rescue him, but is killed when Truth shoots her in the back with a Brute Spiker.

Miranda Keyes was voiced by Julie Benz in Halo 2, but Bungie recast the role for Halo 3, ostensibly because they wanted someone with an accent.[29] Despite not being a part of Halo 3, Benz said that she loved voiceover work and that it was pure chance she had become the voice of Keyes in the first place.[30] When IGN asked Benz what she thought of her character, she admitted she hadn't played Halo 2, even though Bungie had sent her copies of the game.[30] The character is voiced by Justis Bolding in Halo 3.

Dr. Catherine Elizabeth Halsey is a civilian scientist in the United Nations Space Command. A flash clone of her brain is the basis for the construction of Cortana.[31] As the creator of the SPARTAN-II Project, she is responsible for 75 of the 150 Spartan children, along with their training and the subsequent death of 30 due to the dangerous augmentation process.[32] She is viewed by the SPARTAN-IIs as a "mother" figure, preferring to address each of them by their name rather than numerical designation, and knows each Spartan well enough that she can identify them individually by their mannerisms when they are fully suited in their armor, and otherwise indistinguishable from one-other.[33] Halsey justifies her actions through her belief that the suffering of a few is acceptable for the benefit of many. Sergeant Johnson, however, unknowingly causes Halsey to rethink her position, and she decides to "save each and every member of humanity beginning with herself" during Halo: First Strike.[34] She hijacks a shuttle for her own private mission to the planet Onyx;[35] there, she assists in deciphering the surrounding Forerunner glyphs on the planet and leads the surviving Spartan-IIs and Spartan-IIIs to a Dyson Sphere at the heart of Onyx. She and the Spartans are later freed from Onyx, but Halsey is arrested for "committing acts likely to aid the enemy" by kidnapping Kelly-087 and telling Lord Hood to send more Spartans to Onyx.[36] She is later branded a war criminal.[37] She is later revealed to be the mother of Miranda Keyes. During the events on Requiem, she is called in to help and forms an alliance with Jul 'Mdama, particularly after Commander Sarah Palmer tries to assassinate her. During this time, she also learns from the ship's AI Roland, to her shock, that the Master Chief survived and was even on board the Infinity which no one told her, something that shocks and angers Halsey due to how deeply she cares for the Master Chief.[37] She subsequently helps Jul during the search for the Absolute Record,[38] but later defects back to the UNSC after discovering the threat posed by Cortana. Halsey helps fight the Covenant remnants on Sanghelios and to launch the Guardian so that Fireteam Osiris can reach Cortana and Blue Team. After the Spartans return, Halsey is reunited with the Master Chief for the first time in years.[39] She is voiced by Jen Taylor, who also voices Cortana, in Halo: Reach, Halo 4, and Halo 5: Guardians. Taylor also provides motion-capture performance for Halsey in Halo 4 and Halo 5.[40] The character is voiced by Shelly Calene-Black in Halo Legends. Natascha McElhone will portray the character in the upcoming Showtime series.[41]

Colonel James Ackerson is a high-ranking UNSC Army officer, who acts as a connection between the army and Office of Naval Intelligence. He has seen many years of service and has survived several battles with the Covenant. Such is his influence that he dominates the Security Committee and can talk down most higher-ranking officers without fear of reprisal.[42] Due to the competition between Ackerson and other departments, most notably Section Three and the SPARTAN-II project, Ackerson harbors a strong resentment toward his opponents and toward the Spartans in particular. He does eventually convince the top members of ONI to approve his SPARTAN-III Program in 2531 as seen in Halo: Ghosts of Onyx. As part of this, he kidnapped Spartan-II Kurt-051, renamed Kurt Ambrose, to lead the program. In Halo: The Fall of Reach, he attempts to sabotage the MJOLNIR Mark V testing process by using ordnance far above the established guidelines, including Lotus anti-tank mines, a full squad of ODSTs ordered to shoot to kill, automated gun turrets, and an airstrike. However, Cortana retaliates by forging a letter requesting a reassignment to the front lines as well as planting evidence of illicit activities in his bank records. In Halo: First Strike, it is revealed that Ackerson manages to weasel his way out of Cortana's mess and takes part in a Security Council meeting regarding the destruction of Reach.[43] In the limited comic series Halo: Uprising Ackerson falls into the hands of Covenant orbiting Mars and is slated to die before Ackerson tells his interrogator about a "key" to Earth, the Key of Osanalan which he claimed was located in Cleveland, Ohio.[44] Its later revealed that the Key of Osanalan was actually made up by Ackerson and his little brother Ruwan as part of a game when they were children and Ackerson's intention was to prevent the Covenant from destroying Cleveland so his brother could escape. Instead, Ruwan used the deception to help the UNSC strike a blow against the Covenant. In the aftermath, Ackerson taunted his captors about the deception and was decapitated in retaliation.

Senior Chief Petty Officer Franklin Mendez is the SPARTAN-II's trainer on Reach during the early events of Halo: The Fall of Reach. He provides his trainees with excellent weapons and physical lessons, as well as tactical and mental training. He is not very talkative, but possesses a brilliant mind for warfare, and this is reflected in the Master Chief's abilities. He is described as neither tall nor muscular, with close-cut hair that has a dash of gray at the temples.[45] He leaves the Spartans after the discovery of the Covenant to train the next batch of Spartans,[46] and is recruited by Colonel Ackerson to assist Lieutenant Commander Kurt Ambrose (Spartan-II Kurt-051) with training the SPARTAN-III supersoldiers at the secret world of Onyx after a few years of combat duty (receiving two Purple Hearts in the process).[47] During Ghosts of Onyx he is sealed inside the Forerunner Dyson Sphere at the heart of the planet with the remaining Spartan survivors.[48] In Halo: Glasslands, after bringing the shield world out of slipspace, the group was rescued by Kilo-Five led by Captain Serin Osman, a former Spartan-II who "washed out" of the program due to augmentation issues and was then recruited into ONI.

Fleet Admiral Lord Terrence Hood (voiced by Ron Perlman) first appears in the novel Halo: First Strike. He the Chairman of the UNSC Security Council and is the highest-ranking officer in the UNSC Navy: the Chief of Naval Operations.[49] He greatly respects the Spartans, not only because of their record, but because they have saved his life on two occasions.[42] When Halo 2 begins, Admiral Hood presents the Master Chief, Sergeant Johnson, and Miranda Keyes with medals aboard the Cairo Station. In Halo: Ghosts of Onyx, Hood receives an urgent message by Dr. Halsey requesting for him to send Spartans to assist her, and obliges by ordering Fred-104, Will-043, and Linda-058 to Onyx. In Halo 3, Hood is in overall command of Earth's defense following the death of Fleet Admiral Harper and shares command with Commander Miranda Keyes, who reports directly to him. He accepts the need for humanity to ally with the Elites, but is not entirely happy about it. He leads the remaining human naval forces in an attack on the Prophet of Truth's dreadnought,[50] but the attack fails when the Forerunner artifact under New Mombasa activates, creating a portal to the Ark. When the Master Chief, Keyes, and several Elite and human forces choose to follow the Prophet of Truth through the portal, he decides to stay behind to make a final stand on Earth.[51] At the end of the game, he commemorates a small monument to the war and the sacrifices it involved. Though unable to forgive the Arbiter for his actions during the war, Hood thanks him for standing by the Master Chief "to the end" and expresses sorrow at the Spartan's apparent death. Hood also appears in the spin-off media, including several of the books and comics which delve further into his backstory. Its revealed that Hood was captain of a ship during the Battle for Arcadia in Halo Wars and was ordered to collect the Spirit of Fire's log buoy, but instead attacked a Covenant destroyer, resulting in its loss. Hood subsequently blamed himself for the loss of the Spirit of Fire. In Halo: Renegades, John Forge's daughter finds the wreck of Hood's old ship and captain's logs by Hood's successor pointing to the destroyer having subsequently recovered the buoy, leading to her own search for the Spirit of Fire. In the short story "Rosbach's World" taking place after Halo 5: Guardians, Hood is revealed to have escaped Cortana's attack on Earth along with Admiral Serin Osman of ONI thanks to preparations set up in secret by Osman's still-loyal AI Black Box. The two are also able to escape with many of ONI's AIs in their possession, leaving Osman with the dilemma of whether or not to destroy them or risk the AIs defecting to Cortana. However, Hood blames himself for the situation due to allowing the Master Chief free rein and falls into a depression.

Private First Class Wallace A. Jenkins is one of the UNSC forces that survives the initial Covenant attack in Halo: Combat Evolved. Halo: Contact Harvest reveals that the Marine was a member of the colony Harvest's defense militia, where his family is killed. In Halo: The Flood, Jenkins assists in defending the human stronghold under the command of Major Antonio Silva. He is also part of an assault team led by Sergeant Avery Johnson and Captain Jacob Keyes, sent to recover a Covenant arms cache during Halo: Combat Evolved. The team is overwhelmed by the Flood, leaving the entire squad except Sergeant Johnson infected and resulting in the eventual death of Captain Keyes. In the video game, the Master Chief recovers Jenkins' helmet, and reviews the recording of the mission that it contained, introducing the Flood to the player through the Marine's eyes. In Halo: Combat Evolved, the fate of the Marine is left unknown.

Halo: The Flood reveals the fate of Jenkins; the Private is transformed into a Flood Combat Form along with the rest of his squad, but he is able to exercise a certain degree of control over the infection, due to the mind of the parasite being weakened by its long hibernation.[52] He uses this limited control in an attempt to end his own life, charging at UNSC Marines in the hope that they would shoot him.[53] Instead, he is captured as a live specimen for study. He is brought aboard the Covenant cruiser Truth and Reconciliation as part of a mission under Orbital Drop Shock Trooper Major Silva to capture a Covenant vessel and return it to Earth intact. Jenkins successfully convinces Lieutenant Melissa McKay, that such a mission would spread the Flood to Earth, and Jenkins dies with the other human troops on the vessel as it crashed into Halo.[54]

Admiral Serin Osman is the head of ONI by 2558 and also a former Spartan-II during which time she was known as Serin-019. Unlike most of the Spartans, Osman's augmentations didn't take, though she wasn't left physically debilitated like most of the other "wash-outs." Admiral Margret Parangorsky, the head of ONI at the time, saw promise in Osman and reversed her augmentations and gave her a career in ONI instead. Unable to remember her real last name, she was given the last name of Osman by Parangorsky and groomed to be her successor.

In the Kilo-Five Trilogy, Osman, a Captain at the time, leads the black ops team Kilo-Five who are sent on covert operations in the post-war period. ONI uses the team to cause chaos between the various Covenant factions in an attempt to keep any one from gaining too much power and filling the power vacuum left by the fall of the Covenant Empire. After the Onyx shield world is discovered, Osman and her team arrest Dr. Catherine Halsey for war crimes and imprison the captured Jul 'Mdama on Onyx before he manages to escape. The team also comes up against the father of one of their members who is seeking revenge for the presumed death of his daughter. They subsequently decide to cover up his survival, knowing that he is no longer a threat.

By the time of Halo: Last Light, Osman has been promoted to Rear Admiral, though she is not yet in charge of ONI. Osman coordinates with the UNSC forces on Gao and orders Blue Team to drop a nuclear weapon on the underground Forerunner base to keep it out of enemy hands. Osman personally joins the extraction team and gives Veta Lopis the chance to destroy the Forerunner AI Intrepid Eye as a test. Afterwards, Osman removes the Spartan-III's from Blue Team due to the dangers of their augmentations becoming public knowledge, but instead turns them into an investigative team known as the Ferrets led by Lopis. During the Halo: Fractures short story A Necessary Truth, the Ferrets are targeted by Dark Moon Enterprises operatives hoping to expose their augmentations and thus destroy ONI. The Ferrets are able to stop the plot and turn over the evidence they gather to Osman. Though the Ferrets lie to Osman about some of the details of the mission, she decides to accept it despite being somewhat dubious.

In Halo: Retribution, Osman oversees the mission to avenge the murder of an Admiral and the kidnapping of her family. After the mission exposes a dangerous bioweapon plot, apparently done by ONI, Osman gives orders to shut down the project. However, Intrepid Eye, the true culprit, manipulates Osman's final report to give the project an unlimited black budget and continues it in secret on Argent Moon.

In Spartan Ops, Captain Thomas Lasky contacts Osman after Dr. Catherine Halsey is abducted by Jul 'Mdama. Osman laments not following Parangorsky's suggestion of killing Halsey or burying her as deep as she could and orders Lasky to assassinate Halsey.

In the short story Rossbach's World, Osman is revealed to have escaped the subjugation of Earth by Cortana along with Lord Hood thanks to her personal AI Black Box who remained loyal and set up an escape plan for her if needed. Osman and Hood escape with many of ONI's AIs and Osman is left contemplating whether or not to destroy them.

Captain Thomas Lasky is the current captain of the UNSC Infinity and is currently voiced by Darren O'Hare. He made his debut in his origin web series Halo 4: Forward Unto Dawn portrayed by Tom Green as a young military cadet saved by the Master Chief and Ty Olsson as an adult. In Halo 4, Lasky serves as Infinity's first officer at the rank of Commander and aids the Master Chief on Requiem. When Infinity's captain Andrew Del Rio refuses to listen to the Master Chief and Cortana, the Spartan decides to go rogue rather than abandon the fight with the Infinity. Lasky, ordered to stop the Master Chief, instead secretly supports him by providing the Spartan with a combat-outfitted Pelican for his use. When the Master Chief returns to Earth, he discovers that Del Rio has been relieved of command for abandoning the Master Chief and Lasky promoted to Captain as his replacement. Now commanding Infinity, Lasky aids the Master Chief in boarding the Didact's ship. After the Master Chief is rescued from the wreckage, Lasky attempts to comfort the grieving Spartan and reminds him that soldiers aren't machines, they are just people. Six months later, Lasky returns in Spartan Ops, leading the Infinity back to Requiem. After helping defend his ship from a Promethean and Covenant attack, Lasky clashes with Commander Sarah Palmer over orders to assassinate Dr. Catherine Halsey. With Palmer refusing to stand down, Lasky orders Fireteam Majestic to rescue Halsey in an attempt to save her life.

As Captain of the Infinity, Lasky appears in spin-off media, particularly the Halo: Escalation comic series.

Lasky returns in Halo 5: Guardians. After receiving a message from Halsey, Lasky sends Fireteam Osiris to Kamchatka to rescue the doctor and to kill Jul 'Mdama if possible. Following the successful mission, Lasky reluctantly sends Fireteam Osiris after Blue Team on Meridian and later authorizes a covert operation to Sanghelios to seek out the Arbiter's help in chasing Blue Team using a Guardian on the planet. Due to ONI refusing to get involved in the Arbiter's civil war, Lasky is unable to bring Infinity into the fight and warns Spartan Jameson Locke that if something goes wrong, the mission will have never officially existed. When AIs begin pledging loyalty to Cortana en masse, Lasky and Infinity witness the beginning of the subjugation of Earth, though Infinity's AI Roland chooses to remain loyal to humanity. Lasky orders a series of random slipspace jumps, planning to run until they can figure out a way to fight back.

In Halo: Bad Blood, taking place after Halo 5: Guardians, Lasky and Infinity link up with Blue Team and Fireteam Osiris the next day. Along with debriefing the team leaders, Lasky meets with Spartan Edward Buck in a more informal setting and offers the Spartan, who has been ordered on a covert mission even Lasky isn't allowed to know about, advice, particularly regarding leadership. The conversation with Lasky helps settle some of Buck's doubts and issues, many of which stem from the mission requiring Buck to work with an old friend who betrayed his trust. After the mission, Lasky and Palmer debrief Buck and he convinces them to allow Mickey Crespo to remain in the fight, at least until Cortana has been defeated, despite Mickey being in prison for treason.

Roland, voiced by Brian T. Delaney, is the current AI of the UNSC Infinity, the flagship of the UNSC fleet. Roland's avatar takes the form of a golden World War II fighter pilot. Roland first appears in Spartan Ops where he helps plan missions and in some cases, aids the Spartan controllers in leading fireteams on Requiem, something that Roland comes to greatly enjoy. Using an override code, Dr. Catherine Halsey is briefly able to take control of Roland and force him to help her, learning from the AI that the Master Chief is in fact still alive and was even on Infinity which no one had informed Dr. Halsey of. However, before Dr. Halsey can escape to meet up with Jul 'Mdama, Roland manages to regain control of himself and expose Dr. Halsey's deception to the guards before a Promethean attack on the ship captures the doctor.

Roland appears in spin-off media, including the Halo: Escalation comic series, Halo: Fractures and Halo: Tales from Slipspace. Along with acting as Infinity's AI, Roland takes part in fellow AI Iona's "trial" with Black Box and takes part in Fireteam Majestic's poker night.

In Halo: Spartan Assault, Roland takes on the role of a narrator for cadets undergoing battle simulations based on the Battle of Draetheus V in 2554.

In Halo 5: Guardians, Roland continues to act as the Infinity's AI. Roland is outraged when Dr. Halsey returns and makes accusations that, in Roland's own words, could effectively condemn the other AI to death. Roland angrily confronts the doctor on her hypocrisy and the fact that Cortana is being condemned simply for surviving past her normal lifespan. When Cortana subverts many of the AIs of the galaxy to her cause, Roland is one of the very few AIs that remains loyal to humanity instead of pledging his loyalty to Cortana, showing no signs of considering Cortana's offer even when she appears on Infinity's bridge. Roland is shocked when Lasky decides to run, but Lasky explains that they will run until they have a way to fight back.

Roland appears in Halo: Bad Blood, taking place after Halo 5: Guardians. Roland is confirmed to continue to be loyal to humanity which is a good thing due to the amount of control the AI has over Infinity's systems. Roland's ability to see through Cortana's offer for the bad deal it is endears him greatly to Spartan Edward Buck. When Buck and Captain Veronica Dare decide to get married, Roland interrupts their argument about whether or not to do it via a program or call in Captain Lasky as captain of the ship. Roland offers to marry Buck and Dare himself, stating that as the ship's AI, which in many ways effectively makes Roland Infinity, he can perform a marriage as legally as if Lasky did it. Due to his fondness for the AI, Buck accepts and Roland marries the two, ending with "feed the birds!"

Conceived by Halsey, the SPARTAN-II program was secretly commissioned to create an elite corps of supersoldiers who could stem rebellion in the UNSC colonies; these soldiers became the best weapon against the alien Covenant when war broke out. While John-117, also known as the Master Chief, is the hero of the trilogy, other soldiers play a significant role in the novels, Halo Legends, and the prequel games Halo Wars and Halo: Reach. To raise morale as the war continued to sour for humanity, the existence of the SPARTAN-II Program is disclosed to the general public. The Spartans become heroes and veritable legends; in order to maintain public confidence that the war is going well, Spartans are never listed as killed, only as Missing in Action or Wounded in Action.[55] The SPARTANS were kidnapped as children, who were replaced by flash clones, which died of natural causes afterwards. The physical augmentation they undergo to turn them into super soldiers is lengthy, expensive, and strenuous, with not all of them surviving the process. Both male and female SPARTANS average 7 feet (2.1 m) tall. After being recruited into the UNSC, the Spartans' last name are disposed of; their callsign is simply their first name, and a corresponding 3-digit figure (for example, Alice-130, Douglas-042, Samuel-034, etc.).

The SPARTAN-III Project was started by Colonel James Ackerson to serve as cheaper, disposable supersoldiers. Some of these Spartans were main protagonists in the game Halo: Reach, including the player character SPARTAN-B312, aka "Noble Six". Later, the UNSC creates the SPARTAN-IV project. Unlike the SPARTAN-II and -III projects—which kidnapped and conscripted children or used war orphans, respectively—the Spartan-IVs are adult volunteers drawn from all branches of the UNSC. These Spartans participate in war games on the starship Infinity, which forms the fictional basis for Halo 4's multiplayer.[56]

The most distinctive element of the Spartans is their special MJOLNIR powered assault armor. The Mark V armor from Halo: Combat Evolved was ranked third of Casualty Gamer's "Top 10 Bodysuits," with the author commenting "It's one of the most recognizable symbols from any game, and is literally the image of the franchise's legendary hero, Master Chief."[57] The "Recon" armor of Halo 3's multiplayer was also rated tenth of Machinima.com's "Top 10 Video Game Armor,"[58] as well as Maxim's.[59]

Inspired by the Halo video game series, Troy Hurtubise, known for his anti-bear suits, developed a real counterpart to the MJOLNIR powered assault armor,[60] named the Trojan. The suit is functional and its capabilities were inspired by those present in the video games versions of the armor. The armor's features include a system that purifies air, powered by solar panels located in the helmet, equipment for weapon transportation, a recording system, emergency illumination, and a transponder that can be activated if the wearer is in serious jeopardy.[60] The armor offers protection against attacks with knives, blunt objects, and small explosions and is bulletproof.[60] Hurtubise expressed that he is able to improve this design for use in the military for a price of 2,000 dollars per piece.[60] Non-functional replicas of the MJOLNIR powered assault armor have also been created by hobbyists;[61] a Spike TV pre-Halo 3 special profiled some of these dedicated fans.[62]

Commander Sarah Palmer (Jennifer Hale) is a Spartan-IV stationed on UNSC Infinity and the leader of the Spartan IVs. She appears in Halo 4, Halo 5: Guardians, Halo: Spartan Assault, and the Halo Escalation comic series.

Gunnery Sergeant Edward Malcolm Buck (Nathan Fillion) is a longtime human soldier. In Halo 3: ODST he is the leader of Alpha-Nine, a squad of Orbital Drop Shock Troopers (ODSTs). He is subsequently inducted into the SPARTAN-IV program, and is a playable member of Fireteam Osiris in the video game Halo 5. He makes a brief appearance in Halo: Reach and is the main character of the novels Halo: New Blood and Halo: Bad Blood. In the latter, Buck reunites his old squad Alpha-Nine for a classified ONI mission following the events of Halo 5 and is reluctantly forced to work with his old friend Mickey Crespo who betrayed Buck's trust and was imprisoned for treason. At the end of the novel, Buck decides to return to leading Alpha-Nine full-time and is married to long-time girlfriend Veronica Dare by Infinity's AI Roland.

Jameson Locke is a Spartan IV who first appeared in Halo 2 Anniversary's both opening and ending with the task of hunting down the Master Chief in Halo 5: Guardians. Mike Colter portrays Locke in both Anniversary and the Nightfall origin movie, and only provided the motion-capture performance for the character in Guardians. Due to scheduling conflicts with Jessica Jones and Luke Cage, Locke's voice acting is replaced by Ike Amadi. He is the current squad leader of Fireteam Osiris, tasked with hunting down Master Chief and Blue Team.

Fred-104, voiced by Andrew Lowe in Halo: Legends, portrayed by Tony Giroux in Halo 4: Forward Unto Dawn and Travis Willingham in the Halo 2: Anniversary Terminals and in Halo 5: Guardians, is a Spartan-II and one of the Master Chief's closest friends.

Fred survives the fall of Reach, as shown in Halo: First Strike, and assists Master Chief and other Spartans in destroying a Covenant armada massing to attack Earth. In Halo: Ghosts of Onyx, Fred and Blue Team help defend the Earth from Covenant attack during the events of Halo 2 while the Master Chief is away on the second Halo ring. Following a message from Halsey, Blue Team hijacks a Covenant destroyer to travel to the planet Onyx where Halsey and the Spartan-III's are located. There, Blue Team is reunited with both Kelly and the Spartan-III leader, Lieutenant Commander Kurt Ambrose, an old friend theirs believed to be dead for nearly twenty years. Under heavy Covenant and Sentinel attack, the group takes out a Sentinel factory on the planet and defends the entrance to the interior shield world. Ultimately, Kurt decides to sacrifice himself to destroy the Covenant ground forces with nuclear weapons. Before sending the others through the portal, Kurt promotes Fred to the rank of Lieutenant, Junior Grade. Afterwards, Fred and the others mourn those they lost in the battle and prepare to explore the world they are now on. They reconnect with the outside world in Halo: Glasslands; though to them only a few days have passed, outside months have.

Fred continues to serve in the post-Covenant War Spartan branch. In Halo: Last Light, Fred and Blue Team investigate a Forerunner structure on the politically-unstable planet of Gao and get caught in both the machinations of a power hungry leader and the plans of a rogue Forerunner AI, Intrepid Eye. This pits the UNSC against the Covenant splinter faction known as the Keepers of the One Freedom which Gao's Minister of Protection, Arlo Casille, uses to gain power and turn on the UNSC, having secretly brought the Keepers to the planet for just that purpose. Intrepid Eye destroys Fred's AI Wendell and nearly escapes using Fred's armor, but Veta Lopis, a Gao investigator who was investigating a series of murders committed by Intrepid Eye, disables Fred's suit with an explosive she had earlier planted and the rogue AI is captured. Fleeing the planet, Blue Team destroys the Forerunner base with a nuclear weapon, but Admiral Serin Osman, herself a former Spartan-II, removes the Spartan-III's from the team due to the danger if their illegal augmentations are exposed. Instead, Osman turns the III's into an investigative team known as the Ferrets led by Lopis.

In Halo: Retribution, Fred is given tactical command of a mission to avenge the murder of an Admiral and the kidnapping of her family, apparently by the Keepers of the One Freedom. Blue Team works alongside the Ferrets who manage to infiltrate a Keeper base, but discover the Admiral's family dead. Blue Team provides backup and destroys the base with nuclear weapons, but it's discovered that the bodies were planted. The investigation leads them back to Gao and ultimately to Meridian where the group exposes and foils a dangerous bioweapon plot, unaware that the true culprit was Intrepid Eye.

In the Halo: Escalation comic series, Fred and the other members of Blue Team are reunited with the Master Chief who had survived the final battle with the Covenant and made it back to Earth after over four and a half years. Despite being the ranking officer as a Lieutenant, Junior Grade, Fred returns control of the team to the Master Chief and returns to his old role as second-in-command. Together, they defeat the returned Didact and go on a series of non-stop missions.

Fred appears alongside the Master Chief, Kelly and Linda in Halo 5: Guardians.

Linda-058 (voiced by Andrea Bogart in the Halo 2: Anniversary terminals and Brittany Uomoleale in Halo 5: Guardians) is the sniper of the Spartan-II's and one of the Master Chief's closest friends. Linda is notable for her exceptional sniping skills and ability to make seemingly impossible shots. Ironically, she has a non-existent temper. She is also notable for being clinically dead for several weeks after being mortally wounded during the Fall of Reach. She appears in both much of the spin-off media and Halo 5: Guardians.

In Halo: The Fall of Reach, Linda takes part in the Spartans first mission to capture a rebel leader, but is one of the Spartans to miss the Covenant ship they board to destroy it from the inside. Later, during the Fall of Reach, Linda accompanies the Master Chief and another Spartan, James, to Reach Station Gamma to destroy an unsecured navigation database. James is blown into space and presumably killed while the Master Chief and Linda succeed in completing their mission with the help of some Marines on the station, including Sergeant Avery Johnson. However, while securing their exit, Linda is hit by Covenant fire and mortally wounded. She dies in the Master Chief's arms after confirming that they had succeeded. Despite this, the Master Chief places Linda into a cryo-chamber immediately upon returning to the Pillar of Autumn, believing that, while its a long shot, due to her resilience as a Spartan, Linda might be able to be revived if they can get her to a UNSC hospital. However, this plan is foiled by the loss of Reach and the need to flee the system.

In Halo: First Strike, the Master Chief and Cortana recover several ejected cryo-chambers from the wreckage of Halo, the Pillar of Autumn having ejected some occupants who hadn't been awakened before the ship crashed. One of these chambers and the only one to still be functional is Linda's as the Master Chief later discovers. Due to her state, the Master Chief leaves Linda in the chamber until they can hopefully get her to a hospital. After being rescued along with several other survivors of the Fall of Reach, Dr. Catherine Halsey decides to use the medical facilities on board the salvaged UNSC frigate Gettysburg to try to save Linda's life due to the recently discovered threat to Earth from the Covenant. Cloning several replacement organs for her, Halsey successfully manages to revive Linda who she predicts will need weeks to properly recover from her injuries. Despite this, Linda is able to be up and about in a short amount of time to join her friends in planning a first strike against the Covenant, though she is still visibly suffering the effects of her near-fatal injuries. Despite Linda's weakened state, she is allowed to join the operation due to the limited number of available Spartans and her unique sniper skills. Linda's sniper abilities prove invaluable on the mission which proves to be a success, decimating the Covenant fleet that is poised to attack Earth and buying the human race some more time. However, during this time, Kelly is kidnapped by Halsey who vanishes with her off to parts unknown.

In Halo: Ghosts of Onyx, a fully recovered Linda and Blue Team help defend the Earth from Covenant attack during the events of Halo 2 while the Master Chief is away on the second Halo ring. Following a message from Halsey, Blue Team hijacks a Covenant destroyer to travel to the planet Onyx where Halsey and the Spartan-III's are located. There, Blue Team is reunited with both Kelly and the Spartan-III leader, Lieutenant Commander Kurt Ambrose, an old friend theirs believed to be dead for nearly twenty years. Under heavy Covenant and Sentinel attack, the group takes out a Sentinel factory on the planet and defends the entrance to the interior shield world. Ultimately, Kurt decides to sacrifice himself to destroy the Covenant ground forces with nuclear weapons. Afterwards, Linda and the others mourn those they lost in the battle and prepare to explore the world they are now on.

In Halo: Glasslands, the Spartans are able to make contact with several Huragok in the shield world and convince them to bring it out of slipspace. The group is then rescued what to them is a few days later, but to the rest of the universe, months later. To their relief, they discover that the Covenant has been defeated, but the Master Chief apparently perished in the final battle. Blue Team, now made up of both the survivors of the original team and the surviving Spartan-III's, decide to join the new Spartan branch and continue serving in the post-war universe.

In Halo: Last Light, Linda and Blue Team investigate a Forerunner structure on the politically-unstable planet of Gao and get caught in both the machinations of a power hungry leader and the plans of a rogue Forerunner AI, Intrepid Eye. This pits the UNSC against the Covenant splinter faction known as the Keepers of the One Freedom which Gao's Minister of Protection, Arlo Casille, uses to gain power and turn on the UNSC, having secretly brought the Keepers to the planet for just that purpose. Intrepid Eye destroys Fred's AI Wendell and nearly escapes using Fred's armor, but Veta Lopis, a Gao investigator who was investigating a series of murders committed by Intrepid Eye, disables Fred's suit with an explosive she had earlier planted and the rogue AI is captured. Fleeing the planet, Blue Team destroys the Forerunner base with a nuclear weapon, but Admiral Serin Osman, herself a former Spartan-II, removes the Spartan-III's from the team due to the danger if their illegal augmentations are exposed. Instead, Osman turns the III's into an investigative team known as the Ferrets led by Lopis.

In Halo: Retribution, Blue Team is given a mission to avenge the murder of an Admiral and the kidnapping of her family, apparently by the Keepers of the One Freedom. Blue Team works alongside the Ferrets who manage to infiltrate a Keeper base, but discover the Admiral's family dead. Blue Team provides backup and destroys the base with nuclear weapons which are rearmed by Linda, but its discovered that the bodies were planted. The investigation leads them back to Gao and ultimately to Meridian where the group exposes and foils a dangerous bioweapon plot, unaware that the true culprit was Intrepid Eye.

In the Halo: Escalation comic series, Linda and the other members of Blue Team are reunited with the Master Chief who had survived the final battle with the Covenant and made it back to Earth after over four and a half years. Together, they defeat the returned Didact and go on a series of non-stop missions.

In the Halo: Lone Wolf comics, Linda is sent on a solo mission to assassinate the traitorous Dr. Chen. However, her original mission is superseded by ONI with a mission to retrieve the AI Gabriella, thought lost with the UNSC Promise of Dawn during the Fall of Reach. The recovery of Gabriella is important as she is the only AI implanted with all of human history. Linda was forced to combat both Chen and a Covenant splinter faction to retrieve the AI, attempting to convince Chen's followers to leave the planet and avoiding repeated treachery by the doctor. After disabling Chen, Linda chose not to kill him and he had his followers leave with her while Chen sacrificed himself to set off the Promise of Dawn's self-destruct, creating an avalanche that buried the attacking Covenant forces. Linda and the survivors escaped the planet and she was able to return Gabriella to ONI. Though ONI was initially less than pleased with Linda's choices, the support of her AI Athos caused them to chalk it up to the ends justifying the means.

Linda appears alongside the Master Chief, Kelly and Fred in Halo 5: Guardians.

Kelly-087, voiced by Luci Christian in Halo: Legends, Jenna Berman in Halo 4: Forward Unto Dawn and Michelle Lukes in Halo 5: Guardians, is the Spartan-II's scout and the Master Chief's best friend. Kelly is noted for her incredible speed, something that she had even before she underwent augmentation which only increased her speed. She is also notable for being one of the very few Spartan-II's to ever truly be Missing in Action rather than being declared as such to keep up the appearance that the Spartans are invincible. Kelly appears in much of the spin-off media and Halo 5: Guardians. She also acts as the narrator for the animated version of Halo: The Fall of Reach.

In Halo: The Fall of Reach, the Master Chief meets Kelly and fellow trainee Sam on their very first day of Spartan training. Initially, Kelly and Sam hate the Master Chief because his refusal to work as a team on a training exercise gets them into trouble, but the three quickly become best friends. Kelly quickly establishes herself as the Spartans scout due to her incredible speed which no one else can match. When the Spartans undergo augmentation, Kelly barely survives and is the slowest to recover, creating fears that she won't make it. However, Kelly pulls through in the end and joins the Spartans first real mission to capture a rebel leader and is part of the team that makes it aboard a Covenant ship to destroy it after the Spartans receive their armor. However, that mission ends up costing Sam his life. Along with most of the other Spartans, Kelly is sent to Reach's surface to defend the planet from the Covenant and is presumed killed when Reach falls to the Covenant.

In Halo: First Strike, Kelly is revealed to have survived the Fall of Reach, but is one of the very few Spartans to do so. Kelly joins Fred and another Spartan Joshua on a mission to destroy a Covenant cruiser that, although successful, costs them Joshua and in the long run has no impact on the outcome of the battle. Kelly is seriously injured at some point, either during the Spartans' crash-landing, the attack on the cruiser, or the subsequent flight to Castle Base, but she hides this fact from everyone else. At the base, the Spartans are reunited with Dr. Catherine Halsey who treats Kelly's injuries and they flee into a nearby mine to avoid Covenant forces where they recover a Forerunner crystal. Kelly is once again severely injured by the assault cannons of multiple Covenant Hunters with burns to seventy-two percent of her body, but the group is rescued by friendly forces led by the Master Chief. Kelly's injuries keep her out of the fight to defend the captured Covenant flagship Ascendant Justice, but Halsey is able to treat her using the medical facilities aboard the salvaged frigate Gettysburg. Under the guise of a secret mission, Halsey subsequently kidnaps Kelly and flees in a stolen rebel starship to an unknown destination. Following the success of Operation: First Strike, the Master Chief officially declares Kelly Missing in Action.

In Halo: Ghosts of Onyx, Halsey transports herself and Kelly to the planet Onyx which Halsey had discovered was the training grounds for the Spartan-IIIs. Crashing on Onyx, Halsey and Kelly get caught up in the conflict between the local forces and Onyx's Sentinels and Kelly is reunited with the Spartans commander Kurt Ambrose, a Spartan-II who was kidnapped years earlier by ONI to train the new Spartans and Franklin Mendez, the Spartan-II's old trainer. Having decided to save as many Spartans as she can, Halsey had kidnapped Kelly in an attempt to protect her by taking Kelly and as many of the Spartan-IIIs away from the fighting as possible. Halsey manages to transmit a message to Earth that brings the rest of Blue Team, minus the Master Chief, to Onyx. Caught in a three-way battle between the Covenant and Forerunner constructs, the surviving Spartans retreat through a portal to Onyx's interior shield world while Kurt sacrifices himself to destroy the Covenant forces with nuclear weapons. After holding a memorial for those they lost, the Spartans prepare to explore the shield world.

In Halo: Glasslands, the Spartans are able to make contact with several Huragok in the shield world and convince them to bring it out of slipspace. The group is then rescued what to them is a few days later, but to the rest of the universe, months later. To their relief, they discover that the Covenant has been defeated, but the Master Chief apparently perished in the final battle. Blue Team, now made up of both the survivors of the original team and the surviving Spartan-III's, decide to join the new Spartan branch and continue serving in the post-war universe.

In Halo: Last Light, Kelly and Blue Team investigate a Forerunner structure on the politically-unstable planet of Gao and get caught in both the machinations of a power hungry leader and the plans of a rogue Forerunner AI, Intrepid Eye. This pits the UNSC against the Covenant splinter faction known as the Keepers of the One Freedom which Gao's Minister of Protection, Arlo Casille, uses to gain power and turn on the UNSC, having secretly brought the Keepers to the planet for just that purpose. Intrepid Eye destroys Fred's AI Wendell and nearly escapes using Fred's armor, but Veta Lopis, a Gao investigator who was investigating a series of murders committed by Intrepid Eye, disables Fred's suit with an explosive she had earlier planted and the rogue AI is captured. Fleeing the planet, Blue Team destroys the Forerunner base with a nuclear weapon, but Admiral Serin Osman, herself a former Spartan-II, removes the Spartan-III's from the team due to the danger if their illegal augmentations are exposed. Instead, Osman turns the III's into an investigative team known as the Ferrets led by Lopis.

In Halo: Retribution, Blue Team is given a mission to avenge the murder of an Admiral and the kidnapping of her family, apparently by the Keepers of the One Freedom. Blue Team works alongside the Ferrets who manage to infiltrate a Keeper base, but discover the Admiral's family dead. Blue Team provides backup and destroys the base with nuclear weapons which are rearmed by Linda, but its discovered that the bodies were planted. The investigation leads them back to Gao and ultimately to Meridian where the group exposes and foils a dangerous bioweapon plot, unaware that the true culprit was Intrepid Eye.

In the Halo: Escalation comic series, Kelly and the other members of Blue Team are reunited with the Master Chief who had survived the final battle with the Covenant and made it back to Earth after over four and a half years. Together, they defeat the returned Didact and go on a series of non-stop missions.

Kelly appears alongside the Master Chief, Linda and Fred in Halo 5: Guardians.

Two of the Hierarchs, Regret (left) and Truth (right), consult

High Prophets, or Hierarchs, are the supreme leaders of the theocratic Covenant. Upon assuming office, each Hierarch picks a new regnal name from a list of names of former Hierarchs, similar to the practice of some Orthodox Patriarchs.[63] In Halo 2, there are shown to be only three; the Prophets of Truth, Mercy, and Regret (voiced by Michael Wincott, Hamilton Camp and Robin Atkin Downes in Halo 2, respectively; in Halo 3, Truth is voiced by Terence Stamp). The novel Halo: Contact Harvest reveals that these three Prophets, originally known as the Minister of Fortitude, the Vice-Minister of Tranquility, and the Philologist,[64] plotted to usurp the throne of the Hierarchs; in the process, they hide the truth that humanity is descended from the Covenant gods, the Forerunners, believing that the revelation could shatter the Covenant. During the course of Halo 2, Regret attacks Earth, and then retreats to Delta Halo. There, he calls for reinforcements, but is killed by the Master Chief. Later, Mercy is attacked by the Flood on High Charity; Truth could have saved him, but left him to die so he could have full control over the Covenant. In Halo 3: ODST, Truth is seen inspecting some Engineers around the Forerunner construct near New Mombasa. In Halo 3, Truth also meets his demise at the hands of the Arbiter when the Prophet attempts to activate all the Halo rings from the Ark. His death become the culmination of the Covenant's downfall.

Preliminary designs for the Prophets, including the Hierarchs, were done by artist Shi Kai Wang. According to The Art of Halo, the Prophets were designed to look feeble, yet sinister.[65] Originally, the Prophets appeared to be fused to the special hovering thrones they use for transport;[65] even in the final designs, the Prophets are made to be dependent on their technology. Special headdresses, stylized differently for each of the Hierarchs, adds personality to the aliens and a regal presence.[66]

The Arbiter is a rank given to special Covenant Elite soldiers who undertake suicidal missions on behalf of the Hierarchs to gain honor upon their death. They are revered amongst the Covenant for their bravery and skills. In Halo 2, the rank of Arbiter is given to Thel 'Vadamee, the disgraced former Supreme Commander of the Fleet of Particular Justice, which was responsible for destroying Reach. It was under his watch that Installation 04 was destroyed in Halo: Combat Evolved and the Ascendant Justice was captured by the Master Chief in Halo: First Strike. Rather than killing him, the Prophets allow the Commander to become the Arbiter, and to carry on his missions as the "Blade of the Prophets."[67] Eventually, the Arbiter rebels against the Prophets during the Great Schism by dropping the "-ee" suffix from his surname as a symbol of his resignation from the Covenant, and joins his fellow Elites in siding with humanity and stopping the Halo array from firing. Some of his backstory is featured in Halo: The Cole Protocol set about fifteen years before Combat Evolved where the Arbiter, then Shipmaster Thel 'Vadamee, comes into conflict with UNSC forces led by then-Lieutenant Jacob Keyes. The events sow the seeds of doubt in the future Arbiter's mind about the Prophets and their plans. This particular Arbiter is voiced by Keith David.

Originally to be named "Dervish,"[68] the Arbiter was a playable character intended to be a major plot twist by Bungie.[69] Reception to the character was lukewarm, with critics alternatively praising the added dimension brought by the Arbiter[70][71] as well as complaining about having to play as the alien.[72]

In Halo Wars, set 20 years before Halo: Combat Evolved, a predecessor Arbiter is shown, possibly as the last to wear the armor before the more recognized character. He is described as a "mean guy," lead designer David Pottinger comparing him to Darth Vader.[73] This preceding Arbiter is the main antagonist of Halo Wars. Working directly under the Prophet of Regret, he is assigned to lead the destruction of humanity and investigates a structure on the planet Harvest where his attempt to destroy it is foiled by forces led by Sergeant John Forge. He is later ordered by the Prophet of Regret to kidnap Professor Ellen Anders to activate a massive Forerunner fleet on a shield world. He comes into direct conflict with Forge twice, once when the Arbiter kidnaps Anders and a second time when Forge and a team of Spartans attempt to destroy the Forerunner planet and the fleet. After a brutal fight, the Arbiter nearly kills Forge who tricks the warrior before seriously wounding him with Forge's combat knife. Forge kills the Arbiter with one of his own energy swords and a Spartan rolls the Arbiter's body off of a cliff. Like the more well-known Arbiter, his history is somewhat explored in the expanded canon which reveals him to be a disgraced warrior named Ripa 'Moramee who was spared from execution by the Prophet of Regret and made into an Arbiter due to his ruthlessness and likelihood not to question his mission. This particular Arbiter is voiced by David Sobolov.

Making his debut in Halo 2, Special Ops Commander Rtas 'Vadum is never named in the game itself, leading to the unofficial nickname of "Half-Jaw" by fans,[74] due to the missing mandibles on the left side of his face. With the release of The Halo Graphic Novel, however, the character was finally named in the story Last Voyage of the Infinite Succor as Rtas 'Vadumee. The character is voiced by Robert Davi.

'Vadum, originally 'Vadumee before the Covenant Civil War, is a veteran Covenant Elite and the second most prominent Elite character in the series after the Arbiter. He carries the Covenant rank of Shipmaster. The Last Voyage of the Infinite Succor explains how he loses his left mandibles; he is injured after fighting one of his friends, who was infected by the Flood.[75] During the early events of Halo 2, 'Vadumee serves as a messenger between the Hierarchs and the Elite Council, as he is seen relaying messages between the two parties in the Prophets' chamber.[76] Surviving the Prophets' betrayal, 'Vadumee joins his brethren in fighting the Brutes, dropping the "-ee" suffix from his surname to symbolize his resignation from the Covenant. 'Vadum aids the Arbiter in attacking a Brute base to capture a Scarab before departing to take control of a nearby Covenant ship.[77]

In Halo 3, 'Vadum is Shipmaster of the flagship Shadow of Intent, and supports Cortana's plan to follow Truth to the Ark. Along with the Arbiter, 'Vadum leaves Earth to return to the Elite's homeworld with the end of the war. Rtas 'Vadum is known for being a quick, smart, and ingenious tactician and an unparalleled fighter, especially with an Energy Sword and is an excellent leader. He expresses great care for his soldiers, even the Unggoy. He is eager to exact revenge on the Brutes after the Great Schism.

'Vadum appears in the novella Halo: Shadow of Intent taking place after the war. Still the Shipmaster of the Shadow of Intent, 'Vadum protects Sangheili space and comes into conflict with a Covenant splinter faction led by two surviving Prophets, Prelate Tem'Bhetek and the Minister of Preparation Boru'a'Neem. The Prelate is shown to have a personal grudge against 'Vadum, blaming him for the death of his family when High Charity fell to the Flood and 'Vadum had the city partially glassed in a failed effort to contain the Flood. After capturing the Prelate, 'Vadum shows sympathy for him and reveals that the Prelate's family may well have been alive when the Prelate departed the city, meaning that Preparation lied to him. 'Vadum's words shake the Prelate's faith in Preparation who is revealed to be planning to use a prototype Halo ring to destroy Sanghelios using the Shadow of Intent to power it. The Prelate sacrifices himself to stop Preparation, leaving 'Vadum with a new outlook following the encounter. Along with getting the Arbiter to relax age-old rules not allowing females to serve in the military, 'Vadum reveals that he plans to use navigation data recovered from the Prelate's ship to seek out the rest of the Prophets and attempt to determine who should be punished as war criminals and who should be pardoned to coexist in peace as innocents.

Tartarus (voiced by Kevin Michael Richardson) is the Chieftain of the Brutes, easily recognized by his white hair, distinctive mohawk, and massive gravity hammer known as the "Fist of Rukt." Rough, arrogant, and disdainful of the Elites, Tartarus is completely dedicated to the Prophets' salvific "Great Journey." Halo: Contact Harvest reveals that Tartarus became Chieftain after killing the former Chieftain, his uncle Maccabeus, and seizing the Chieftain's weapon. In Contact Harvest, Tartarus acts as one of the main antagonists, working to destroy the human colony of Harvest and coming into conflict with Sergeant Johnson. During the final battle of the novel, Johnson's life is inadvertently saved when one of Tartarus' own soldiers turns against him, damaging Tartarus' armor and forcing him to retreat. Tartarus makes his first appearance in the novel Halo: First Strike, as one of the first Brutes allowed into the chamber of the High Prophet of Truth.[78] In Halo 2, Tartarus acts as an agent of the Prophets, branding the Arbiter for his failures. The Chieftain later appears when the Arbiter tries to retrieve the Activation Index of Delta Halo. On the Prophets' orders, Tartarus takes the Index and pushes the Arbiter to what was intended to be his death in a deep chasm.[79] Tartarus heads to the control room of Halo with the Index in order to activate Halo, but is confronted by the Arbiter. Blind to the Prophets' deception about the Great Journey, Tartarus activates the ring; the Brute is ultimately killed by the coordinated efforts of the Arbiter with the help of Sergeant Major Johnson, successfully preventing the firing of Delta Halo.

Designs for Tartarus began after the basic shape and design of the common Brutes was complete.[80] Artist Shi Kai Wang added small but distinctive changes to Tartarus' armor and mane in order to distinguish the Chieftain from the other Brutes.[81] The visual design of the Chieftains was later modified for Halo 3, with the seasoned warriors sporting more elaborate headdresses and shoulder pads.[5] In a review of the character, UGO Networks noted that whereas the Elites "are a precision scalpel," Tartarus was a "baseball bat" that smashes everything in its path, a reference to their ceremonial weapons, the Energy Sword and Gravity Hammer, respectively.[82]

Jul 'Mdama, voiced by Travis Willingham, is the Supreme Leader of a newly formed Covenant splinter faction following the defeat of the Covenant Empire in Halo 3. Calling himself "the Didact's Hand," Jul's faction initially seeks the Forerunner warrior Didact as an ally against humanity. The character appears in Karen Traviss' Kilo-5 trilogy of novels, as well as Halo 4 and Halo 5: Guardians.

First appearing in the Kilo-Five trilogy, Jul is depicted as a member of the Servants of the Abiding Truth, a religious Covenant splinter faction that is opposed to the Arbiter and his emerging Swords of Sanghelios government. However, Jul is shown to have only joined the Servants as they were the best equipped to combat the Arbiter and his forces as Jul did not believe humanity would change and must be stopped while the Arbiter wanted to form a lasting alliance with them. The Servants attempt to defeat the Arbiter ended in catastrophe thanks to the intervention of the UNSC Infinity in the battle. Jul was subsequently captured by the Kilo-Five black ops team and imprisoned on the Forerunner shield world of Onyx. Jul eventually escaped using one of the shield world's slipspace portals and traveled to the Sangheili colony world of Hesduros which had been cut off from the goings-on in the galaxy since before the Covenant civil war. By portraying his experiences on the shield world in a religious light, Jul was able to win over the inhabitants, but learned that his wife had been killed. Grief-stricken and blaming humanity, Jul discovered the coordinates to the shield world of Requiem on Hesduros and began building up a massive following, forming a new Sangheili-led Covenant. Jul's Covenant eventually found Requiem, but were trapped outside for three years as depicted in the Halo 4 Terminals because the planet required the presence of a Reclaimer to open.

In Halo 4, the Master Chief arrives at Requiem in the rear half of the Forward Unto Dawn and comes into conflict with Jul and his forces. The Master Chief's presence causes Requiem to finally open, granting Jul's Covenant access to the planet. Jul eventually leads some of his forces into Requiem's core where the Forerunner known as the Didact is imprisoned. The Didact is able to trick the Master Chief into releasing him and Jul bows down before him. Despite the core's subsequent collapse, Jul manages to escape with his life and allies himself with the Didact against the humans from the Infinity. Jul's alliance with the Didact leaves him with the ability to command the Didact's Promethean soldiers even after the Didact's own defeat. Subsequent to this, Jul brands himself "the Didact's Hand" with his status and ability to control the Prometheans giving him even more power and attracting more followers to his cause.

In Spartan Ops, six months after the Battle of Requiem, the Infinity returns to Requiem which is still occupied by Jul and his Covenant. The forces of the Infinity and Jul's forces battle each other for control over the planet while Jul personally leads the attempt to access the Librarian's AI which Jul wants to use for the power that the Librarian can give to him. In Halo: Escalation, Jul and Halsey work together while Jul faces a mutiny inside of his own forces. Their mission to access the Absolute Record of Forerunner installations, however, fails.

In Halo 5: Guardians, Jul's power has begun to break following all of his defeats and his Prometheans turning against him under the influence of Cortana. On the remote world of Kamchatka, Jul attempts to access the Forerunner Domain with the help of Halsey while his loyal forces battle the Prometheans. However, Jul is unaware that Halsey has betrayed his location to the UNSC due to the threat Cortana poses. He is killed by Spartan Jameson Locke in single combat and Jul's Covenant falls apart soon thereafter.

343 Guilty Spark, as he appears in Halo 3

343 Guilty Spark (or Guilty Spark or just Spark) (voiced by Tim Dadabo) is a robot character who appears in the original Halo trilogy. 343 Guilty Spark was originally a human named Chakas who was digitized by the Forerunners at the expense of his biological form. Guilty Spark served as the caretaker of the Halo ring Installation 04, where he was an occasional ally and enemy to the Master Chief. He is ultimately severely damaged when he tries to stop Master Chief from activating Installation 08 to stop the threat of the Flood. A fragment of Spark was recovered by the UNSC, and the AI ended up commandeering the ship to seek out the Librarian and bring back his old friends from when he was human.

In the novel Halo: Renegades, Guilty Spark, now inhabiting the body of a Forerunner armiger robot, is rescued by the salvage crew of the Ace of Spades after crashing on an isolated planet. Having recovered his sanity and much of his human personality, Spark, as he now chooses to go by, is left horrified by what he became as 343 Guilty Spark. Spark allies with the crew to recover their stolen property from ONI who are after the AI as well and to complete his own mission of finding the Librarian. Succeeding in both, Spark is talked out of his original plan by the Librarian and made to recognize the friends he has made amongst the crew. Given a coordinate key to "the safe place" by the Librarian, Spark helps his friends to escape ONI and offers his services to the crew as the shipboard AI for the Ace of Spades which Spark greatly upgrades using Forerunner technology. The crew dedicates themselves to finding the long-lost Spirit of Fire while the Librarian indicates to Captain Rion Forge that Spark, who she calls singularly unique due to his ability to evolve so greatly on his own over time, may still have an important role to play in the events to come.

Bungie originally wanted Guilty Spark to sound similar to the robot C-3PO.[83] Dadabo noted in an interview that reactions to his character have been hostile, finding Spark highly annoying.[11] He described Spark's character as a "bastard" who strings others along in order to accomplish his ends.[83] An annual Halloween pumpkin carving contest named 343 Guilt O'Lantern is organized by Halo.Bungie.Org; both the contest's title and logo use the character's design and name as inspiration.[84] Gaming site GameDaily listed Guilty Spark as one of the top "evil masterminds" of video games, stating "If HAL-9000 had any distant relatives, [Guilty Spark would] be closest of kin."[85]

05-032 Mendicant Bias ("Beggar after Knowledge" as revealed in Halo: Cryptum) was the Contender-class Forerunner A.I. charged with organizing Forerunner defense against the Flood. It was later defected by Gravemind turning it rampant and against the Forerunners, but was eventually defeated after the firing of the Halo array and broken into sections, one of which was taken to the Ark, while another was left on the Forerunner ship that would eventually be incorporated into the Covenant city of High Charity. It is this section of Mendicant Bias that informs the Covenant Hierarchs of the human's descendance from the Forerunners in Halo: Contact Harvest, prompting the Hierarchs to usurp the Covenant leadership and instigate the Human-Covenant War.

Mendicant Bias is first encountered in Halo 3 on the Ark, as it attempted to communicate with the Master Chief through Terminals, claiming it sought atonement for its defection to the Flood by helping the Spartan and may have been destroyed when the Chief activated the incomplete Halo that the Ark was constructing.[86] However, as the Ark survived the firing, albeit badly damaged, Mendicant Bias may have survived as well.

The Didact, born Shadow-of-Sundered-Star, (voiced by Keith Szarabajka) is a Forerunner military leader and the Halo 4's main antagonist. The Didact developed a deep animosity towards humanity after fighting a war with them that cost him many soldiers and his children. The Didact disagrees with the plan to build the Halo Array to fight the Flood, instead proposing a system of "shield worlds" that is ultimately rejected. Going into exile in a kind of stasis within a device known as a Cryptum, he is later awoken by the Forerunner Bornstellar with the help of humans Chakas and Riser, all guided by the Librarian. The Didact imprints his consciousness on Bornstellar, who then becomes the Iso-Didact; when the Ur-Didact is presumed dead after being captured by the Master Builder, Bornstellar assumes the Didact's military role. Unknown to most, the Ur-Didact was actually abandoned in a Flood-infested system where he was captured and tortured by the Gravemind. Though he survived, the Ur-Didact was spurred to more drastic measures in an effort to stop the Flood, forcibly composing humans and turning them into mechanical soldiers. The Librarian incapacitated him and placed him in a Cryptum on his shield world Requiem, hoping that meditation and long exposure to the Domain would amend his motives and heal his mind; however, the activation of the Halos severed the Didact from the Domain, and he spent the next 100 millennia alone, with only his own rage and madness to keep him company.

During the events of Halo 4, the Ur-Didact is accidentally released from his Cryptum by the Master Chief and Cortana. He immediately retakes control of the Prometheans and attempts to digitize the population of Earth, but is stopped by Cortana and Master Chief who is made immune to the Composer by an imprint of the Librarian on Requiem. The comic series Escalation reveals the Didact survived this encounter, but the Spartans of Blue Team stop his plans once again. He is apparently digitized by the Master Chief using several Composers, but the Master Chief considers him contained, not dead.

In Halo: Renegades, 343 Guilty Spark, formerly Bornstellar's human companion Chakas who once helped release the Ur-Didact from his Cryptum, learns from the Librarian of the Ur-Didact's release from his Cryptum on Requiem. From the Librarian's reaction to his questions, Spark realizes that the Ur-Didact's threat is currently "not worrisome" and that the Librarian still hopes for her husband to find peace. However, the Librarian sadly admitted that she believed the Ur-Didact to be beyond redemption.

The Librarian (voiced by Lori Tritel) is a highly ranked Forerunner who is married to the Didact. The Librarian spares humanity from extinction after their war with the Forerunners. She convinces the Forerunner council to use the Halos as preserves for fauna in addition to weapons and manipulates the humans Chakas and Riser as well as the young Forerunner Bornstellar into rescuing her husband from his Cryptum on Earth. She ultimately incapacitates and imprisons the Ur-Didact to stop his plans. While she is presumed to have died when the Halo Array was fired, she uploaded various copies of her personality to aid humanity in assuming the Forerunner's Mantle of Responsibility.

In Halo 4, the Master Chief encounters one such copy on Requiem where the Librarian explains some of the history of the Didact, the war between the humans and the Forerunners as well as the Composer. The Librarian reveals that the Master Chief is "the culmination of a thousand lifetimes of planning," the Librarian having guided humanity through their genetic code to reach the eventuality that became the Master Chief. However, the Librarian is unable to explain what she was planning for before they are interrupted by the Didact. At the Librarian's urging, the Master Chief permits her to accelerate his evolution in order to grant the Master Chief an immunity to the Composer, allowing the Master Chief to survive the Didact's later firing of the weapon. In Spartan Ops, taking place six months later, both the UNSC and Ju 'Mdama's Covenant splinter faction search Requiem for this copy of the Librarian. Dr. Catherine Halsey manages to access a shrine containing the Librarian who provides Halsey with the Janus Key and directs her to find the Absolute Record. The Librarian helps Fireteam Crimson track Halsey's signal in an effort to rescue Halsey from 'Mdama and Crimson helps the Librarian transmit herself to the Absolute Record. She later appears there in Halo: Escalation.

In Halo: Primordium, 343 Guilty Spark, once the human Chakas, claims to know where to find the Librarian, suggesting that she has survived. Rescued from an isolated planet by the crew of the salvage ship Ace of Spades in Halo: Renegades, Spark continues his search for the Librarian, which is ultimately revealed to be a search for another of her copies, not the Librarian herself. In a Forerunner structure on Earth beneath Mount Kilimanjaro, Spark attempts to get the Librarian to help him bring back his friends from when he was human or to join them in the Domain, but the Librarian helps Spark see the folly of his plan. Instead, the Librarian helps Spark recognize the friends he has made amongst the Ace of Spades crew. Though the Librarian offers Spark the chance to join her in joining the rest of her copies at the Absolute Record, he decides to remain behind with his friends. The Librarian provides Spark with a coordinate key to "the safe place" and orders him to "find what's missing. Fix the path. Right what my kind has turned wrong." Before departing, the Librarian seemingly communicates with each member of the crew, telling Captain Rion Forge in particular to look after Spark who is more fragile and important than she could ever know and who might still have a role to play in events to come.

Gravemind (voiced by Dee Bradley Baker) is one of the primary antagonists in the Halo series. The Gravemind is a large, sentient creature of Flood origin, created by the parasite to serve as its central intelligence once a critical biomass has been achieved. It was introduced during the events of Halo 2, where the creature saves both the Master Chief and Arbiter from their deaths, bringing the two face to face in the bowels of Delta Halo. Gravemind reveals to the Arbiter that the "sacred rings" are actually weapons of last resort; a fact the Master Chief confirms.[87] In order to stop Halo from being fired, Gravemind teleports the Master Chief and Arbiter to separate locations, but also uses them as a distraction; Gravemind infests the human ship In Amber Clad, and uses it to invade the Covenant city of High Charity.[88] Capturing Cortana, Gravemind brings High Charity to the Ark in an effort to stop the High Prophet of Truth from activating the Halo network. Although the Master Chief destroys High Charity, Gravemind survives the blast and attempts to rebuild itself on the incomplete Halo.[89] When Halo is activated, Gravemind accepts his fate, but insists that the activation of the ring will only slow, not stop, the Flood.[90] In Halo Wars 2: Awakening the Nightmare, the Gravemind's warning is validated when the Banished inadvertently release a number of surviving Flood forms from High Charity's wreckage. It is also mentioned in the game's menu that while the Gravemind's "most recent physical avatar" was destroyed by the Master Chief, it is "only a matter of time before it rises again". Though the Flood released upon the Ark form a Proto-Gravemind and come close to forming a new Gravemind, the Proto-Gravemind is killed by the Banished and the Flood are once again contained by the Banished and the Ark's Sentinels.

Designed to be a massive, horrifying combination of tentacles and rotting matter,[91] reception to the character was generally mixed. Mike Leonard of the AllXbox community said that the introduction of the "Little Shop of Horrors" reject "ruined the 'cool'" of the Halo franchise.[92] Jeremy Parish of 1UP.com complained that the link between Gravemind and the Flood was never explicitly stated in either Halo 2 or Halo 3 and was hardly seen in the last game.[93]