Order of the Phoenix

Hagrid asks Harry and Hermione for a favour; he expects that he will be sacked soon, and wants them to do something for him if he gets sent away. As he leads them into the forest, he mentions that Firenze working with Dumbledore has made for problems with the Centaurs; they are not happy, especially not with Hagrid as he stopped them kicking Firenze to death. After they have met Grawp and are on their way back out of the forest, they are met by about half a dozen centaurs, including Magorian and Bane; Magorian warns Hagrid that he is not welcome in the Forest any more. As the centaurs do not harm foals (meaning Harry and Hermione), however, Hagrid will be allowed to pass today.

When Harry is trapped in Dolores Umbridge's office along with Hermione, Hermione manages to convince her that Harry was trying to reach Professor Dumbledore to say that the weapon they had been building for him was complete. Umbridge is lured by the promise of this weapon into the Forbidden Forest, where the three of them are challenged by the Centaur herd. While there are many centaurs present, only three are named: Bane, Ronan, and Magorian. It is Magorian who first speaks to the three of them, and who Umbridge attempts to bind.

Deathly Hallows

Magorian is apparently one of the centaurs who joins in at the final battle for Hogwarts.