Muirchertach Ua Briain was one of three sons of Toirdelbach Ua Briain, High King of Ireland,Duffy (2005b); Hudson, B (2005b); Bracken (2004a). a man who secured control of the Kingdom of Munster in the 1060s before gaining the high-kingship of Ireland less than a decade later.Hudson, B (2005b); Jefferies (2005). In 1075, in an act of overlordship over the Kingdom of Dublin, Toirdelbach Ua Briain appointed Muirchertach Ua Briain King of Dublin,MacCotter (2017); Duffy (2005b); Bracken (2004a); Bracken (2004b); Duffy (1993b) p. 15; Duffy (1992) p. 103. following a precedent set by Diarmait mac Maíl na mBó, King of Leinster, a previous claimant to the Irish high-kingship who had done the same to his own eldest son, Murchad, in 1052.Hudson, B (2005a); Hudson, BT (2004); Duffy (1993a) p. 34; Duffy (1993b) pp. 14–15; Duffy (1992) pp. 99–100, 103. When Toirdelbach Ua Briain finally died in 1086, his sons bitterly contested the kingship of Munster before Muirchertach Ua Briain succeeded in securing it for himself.Duffy (2005b); Bracken (2004a); Duffy (1993b) p. 15. By 1091, the latter appears to have regained control of the Dublin,Duffy (2005b); Ryan (1949) pp. 76–77. only to lose it to Gofraid Crobán, King of the Isles,Duffy (1993a) pp. 35–36; Duffy (1992) pp. 108–110; Duffy (1993b) p. 16; Ryan (1949) p. 77. who united it with the Kingdom of the Isles.Duffy (1993b) p. 16. Gofraid's reign in Ireland was short-lived, as Muirchertach Ua Briain forced him from Dublin in 1094. After the Gofraid's death the following year, Muirchertach Ua Briain appointed his own nephew, Domnall mac Taidc, as King of the Isles. Uí Briain influence in the Isles was similarly short-lived, however, as Domnall mac Taidc was apparently forced from the region,Ní Mhaonaigh (2018) p. 146, 146 nn. 83–84; Candon (2006) p. 116; Duffy (2002) p. 57; Duffy (1993b) p. 16; Duffy (1992) pp. 108–110. and Magnús Óláfsson, King of Norway seized control of not only the Isles, but perhaps even Dublin itself, before falling in battle in 1103.Duffy (2002) pp. 57–59; Duffy (1993b) p. 16; Duffy (1992) pp. 110–113. Later in 1111, Domnall mac Taidc temporarily seized the kingship of the Isles in an act that may have been opposed by his aforesaid uncle.Duffy (2002) pp. 57 n. 11, 59; Duffy (1993b) p. 16; Duffy (1992) pp. 114–115. The reasons for Domnall mac Taidc's exit from the Isles are uncertain. Although he may have been forcibly ejected by the Islesmen,Hudson, BT (2005) p. 5. he may well have returned to Ireland to take advantage of Muirchertach Ua Briain's rapidly failing health.Duffy (2002) p. 60; Duffy (1992) p. 115.
