Flaithbertach Ua Néill

Flaithbertach Ua Néill (before 978–1036) was king of Ailech, a kingdom of north-west Ireland. He abdicated in 1030 and undertook a pilgrimage to Rome, for which reason he was known as Flaithbertach an Trostáin (Flaithbertach of the Pilgrim's staff). Following the death of his son Áed in 1033, Flaithbertach left his retirement and resumed the leadership of the Northern Uí Néill.

Flaithbertach, a grandson of Domnall ua Néill, belonged to the northern Cenél nEógain branch of the Northern Uí Néill. The later O'Neill (Irish Ua Néill) kindred, kings of Tír Eógain and later earls of Tyrone, descended from Flaithbertach's branch of Cenél nEógain, and were named for his great-great-grandfather Niall Glúndub. The rival Meic Lochlainn branch of Cenél nEógain, which would be important in the generations after Flaithbertach's lifetime probably descended from Niall Glúndub's brother Domnall mac Áeda. Most of the province of Ulster, from the River Bann in the east to the River Foyle in the west, was ruled by Cenél nEógain and their many clients, of whom the Airgíalla were the most important. Their own lands included much of modern County Tyrone, which bears their name, extending from Lough Neagh to Lough Foyle and northwards to Inishowen. To the east lay the kingdom of Ulster, reduced to little more than modern County Down and southern County Antrim; to the west, Tír Conaill (modern County Donegal) was divided among the branches of another Uí Néill kindred, Cenél Conaill; and to the south the kingdom of Breifne and the kingdom of Mide.

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