(d. 1119), king of Munster, son of Toirdelbach Ua Briain. An ambitious ruler, Muirchertach was arguably the most powerful king in Ireland in his day. Already politically active during the reign of his father, he assumed power on Toirdelbach's death in 1086. Connacht and Mide proved resistant to his over-lordship but he ruthlessly imposed his authority there. Attempts to extend his sway further northwards, however, were less successful, as he faced formidable opposition from the able Cenél nEógain ruler, Domnall Mac Lochlainn. The Irish Sea region provided Muirchertach with another outlet for his political ambition and the kingdom of Man, in particular, claimed his attention. His outward-looking tendencies also brought him into contact with the church reform movement which he sought to promote at the synods of Cashel and Ráith Bressail in 1101 and 1111. Illness in his later years, however, led to his position being considerably weakened by the time of his death in 1119.
From The Oxford Companion to Irish History in Oxford Reference.
Subjects: European History.