Ó Cléirigh

O'Cleary (Irish: Ó Cléirigh) is the surname of a learned Gaelic Irish family. It is the oldest recorded surname in Europe — dating back to 916 CE — and is cognate with cleric and clerk. The O'Clearys are a sept of the Uí Fiachrach dynasty, who ruled the Kingdom of Connacht for nearly two millennia. As Connachta, the O'Cleary's ruled the kingdom of Uí Fiachrach Aidhne for nearly 800 years. They are the descendants of Fiachrae, son of the High King Eochaid Mugmedon, and elder brother of legendary High Kinges Niall of the Nine Hostages. According to legend, they ultimately trace their ancestry back to the mythical Fir Bolg, as well as to Milesius, and consequently to Japheth, son of Noah.

O'Cleary Ó Cléirigh
Parent house	Uí Fiachrach Aidhne
Country	Kingdom of Connacht
Founder	Cleireach mac Ceadach
Final ruler	Mhic Mac Comhaltan Ua Cleirigh
Titles	King of Uí Fiachrach Aidhne Brehons of Tír Chonaill
Cadet branches	Coulton Kilkelly Hynes

During the Norman conquest of Ireland, they were expelled from their land and replaced by their cousins the O'Shaughnessy's. From the early 11th or 12th century, they were based in Tír Chonaill, located in modern-day County Donegal, where they served as poet-historians, scribes and secretaries to the O'Donnell dynasty of Tyrconnell. They authored the Ó Cléirigh Book of Genealogies. The clan Cleary and its branches also appeared in Scotland (sometimes known as McCleary), due to the historical connection and exchange between the two countries, much like the Campbells.