Tigernán Ua Ruairc
Tighearnán Mór Ua Ruairc (older spelling: Tigernán Mór Ua Ruairc), anglicized as Tiernán O'Rourke (fl. 1124-d.1172) ruled the Kingdom of Bréifne as the 19th king in its Ua Ruairc (later O'Rourke) dynasty (964-1605 CE). He was a descendant of Ui Riagain, and one of the provincial kings in Ireland in the twelfth century, constantly expanding his kingdom through shifting alliances, of which the most long-standing was with Toirdelbach Ua Conchobair King of Connacht and High King of Ireland, and subsequently his son and successor Ruaidhri Ua Conchobair. He is known for his role in the expulsion of Diarmait Mac Murchada, King of Leinster, from Ireland in 1166. Mac Murchada's subsequent recruitment of Marcher Lords to assist him in the recovery of his Kingdom of Leinster ultimately led to the Norman Invasion of Ireland.
Read more about Tigernán Ua Ruairc: Early Career, Abduction of Derbforgaill and Norman Invasion of Ireland, Death, Issue