Muircheartach Ua Briain (old spelling: Muirchertach Ua Briain) (also known as Murtaugh O'Brien) (c. 1050 – c. 10 March 1119), son of Toirdelbach Ua Briain and great-grandson of Brian Boru, was King of Munster and later self-declared High King of Ireland. Background and early career Muirchertach Ua Briain was a son of Toirdelbach Ua Briain, the previous Dalcassian King of Munster and de facto High King of Ireland. As a descendant of Brian Boru, he was part of the powerful O'Brien dynasty who ruled Ireland at the time. His mother was Derbforgaill, daughter of Tadhg Mac Giolla Pádraig of Osraige, who also bore Muirchertach's brother Tadhg. His early life is largely unknown. The Annals of Tigernach give his birth date as in the year 1050. Afterwards, he is not mentioned in any of the annals of Ireland until the year 1075 when he was defeated by the Kingdom of Airgíalla in battle near modern Ardee in County Louth, taking heavy losses. This was part of a series of campaigns undertaken by his father Toirdelbach against rebellious lesser kings in the north of the country. He was later appointed as king or governor of the city-state of Dublin by his father. Governor of Dublin Background: Importance of Dublin Despite the victory of Muirchertach's great-grandfather Brian Boru over the Vikings at the Battle of Clontarf in 1014 and the breaking of Norse power in Ireland, Dublin remained under the rule of Norse–Gael kings and had links with other Viking Kingdoms. They paid tribute to their Irish overlords, but otherwise the Irish rarely interfered, mainly because of the trade the Norse brought to the area. However, in 1052, the King of Dublin, Echmarchach mac Ragnaill, was removed by the King of Laigin (Leinster), Diarmuit mac Maíl ma mBó. Echmarchach was replaced by Diarmuit's son, Murchad. As a prince of Leinster, Murchad acted as a sort of governor of the city on behalf of his father, the King. Diarmuit seemed to appreciate the importance of Dublin which, even back then, was recognised as a sort of national capital city and was important for a number of reasons, including trade and its military forces, particularly its navy. Appointment of Muirchertach Following the death of the King of Leinster in the year 1075, Dublin came under the control of Muirchertach's father, Toirdelbach mac Tadhg Ua Briain, King of Munster and High King of Ireland, as he