Muirchertach Ua Briain, King of Munster

Muirchertach Ua Briain
King of Munster
Died	1119
Issue	Mathgamain, Domnall, Bjaðmunjo
House	Uí Briain
Father	Toirdelbach Ua Briain
Mother	Dearbhforgaill ingen Tadhg Mac Giolla Pádraig

Muircheartach Ua Briain (old spelling: Muirchertach Ua Briain) (also known as Murtough O'Brien) (c. 1050 – c. 10 March 1119), son of Toirdelbach Ua Briain and great-grandson of Brian Bóruma, was King of Munster and later self-declared High King of Ireland.

Muirchertach Ó Briain was a son of Toirdelbach Ua Briain, the previous Dalcassian king Munster and de facto high king of Ireland. His mother was Derbforgaill, daughter of Tadhg Mac Giolla Pádraig of Osraige, who also bore Muirchertach's brother Tadhg. In 1086 his father died and the province of Munster from which he had claimed kingship of Ireland had been split between his three sons: Tadhg, Muirchertach and Diarmait. Tadhg died soon after, and Muirchertach banished Diarmait from Munster, claiming its kingship for himself.

Between 1086 and 1101, Muirchertach consolidated and strengthened his position as King of Munster. He went on forays into Mide and Leinster in 1089 and took the kingship of Leinster and fought for the Viking Kingdom of Dublin. In 1093, he accepted the submission of Domnall mac Flainn Ua Maíl Shechnaill, the Uí Néill king of Tara, and also made peace with his brother Diarmait at Cashel.

In 1094, Muirchertach fought the kings of Leth Cuinn and Gofraid Crobán, King of Dublin and the Isles. He went with his army to Dublin and banished Gofraid, and brought about the killing of Domnall Ua Maíl Shechnaill. He asserted supremacy over the Uí Néill kingdom of Mide.

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