(d. 1166), king of Cenél nEógain, eventually penultimate high king of Ireland, came to power in 1136 and by 1149 was in a position to challenge Toirdelbach Ua Conchobair for the kingship of Ireland, a position he held after the latter's death in 1156. His leading ally was Diarmait Mac Murchada of Leinster, and his main rival for the kingship was Rory O'Connor (Ruaidrí Ua Conchobair), whose submission Muirchertach secured in 1161, when the annals declared him ‘king of Ireland without opposition’. When he blinded the king of Ulaid in 1166, Tír Eógain was invaded by the forces of Bréifne and Airgialla, and Muirchertach was killed in battle. His death weakened the Mac Lochlainn family and paved the way for the restoration of the Ó Néills. Since his ally Mac Murchada was immediately banished overseas, it also indirectly brought about the Anglo-Norman invasion of Ireland.
From The Oxford Companion to Irish History in Oxford Reference.
Subjects: European History.