Toirdelbach Ua Briain

Toirdhealbhach Ua Briain (old spelling: Toirdelbach Ua Briain), anglicised Turlough O'Brien (1009 – 14 July 1086), was King of Munster and effectively High King of Ireland. A grandson of Brian Bóruma, Toirdelbach was the son of Tadc mac Briain who was killed in 1023 by his half-brother Donnchad mac Briain.

For the first forty years of his life nothing is known of Toirdelbach. It was not until the 1050s that he found allies in Connacht and in Leinster, particularly the powerful King of Leinster Diarmait mac Maíl na mBó, who would aid his claims to be ruler of Munster. It took perhaps ten years of sustained attack to remove his uncle Donnchad from power, and send him into exile, and to place Toirdelbach in power in Munster as Diarmait's faithful ally.

On Diarmait's death Toirdelbach took over the reins of power, establishing himself as ruler of more than half of Ireland. While not a great military leader, he was a capable politician whose influence extended as far north as Ulaid and who made and unmade Kings of Connacht. He died after more than two decades in power, following a lengthy illness, still in control of events. His son Muirchertach Ua Briain would be the leading king of his day, and his grandson Toirdelbach Ua Conchobair would be greater yet.

Brian Bóruma was the first man in many centuries to establish himself as High King of Ireland almost purely by force of arms. Previous men reckoned High King had belonged to the great Uí Néill kindred, the large group of families who claimed to descend from Niall of the Nine Hostages, which dominated much of central and northern Ireland from the 7th century onwards. No king from the south, where Brian's kindred, the hitherto rather obscure Dál gCais of the region of Tuadmumu (north Munster), had come close to dominating Ireland since the time of Feidlimid mac Crimthainn in the early 9th century, and none had been included in the more widely accepted lists of high kings in historic times. The last effective high king of Ireland from Munster was Cathal mac Finguine (d. 742), and likely before him the prehistoric Crimthann mac Fidaig.

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