Tighearnán Mór Ua Ruairc (older spelling: Tigernán Mór Ua Ruairc), anglicised as Tiernan O'Rourke (fl. 1124–1172) ruled the kingdom of Breifne as the 19th king in its Ua Ruairc (later O'Rourke) dynasty (964–1605 CE), a branch of the Uí Briúin. He was a descendant of Uí 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 Ruaidhrí 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. Early career Ua Ruairc may have ruled Bréifne as early as 1124, as indicated in Mac Carthaigh's Book and the Annals of the Four Masters, the former indicating he allied at the time with the kings of Meath and Leinster against Toirdelbach Ua Conchobair. However the Annals of Ulster and the Annals of Tigernach do not mention him until 1128, where they record his robbing and killing of some of the Archbishop of Armagh's company, the former calling it 'A detestable and unprecedented deed of evil consequence'. He appears to have carried out a number of raids into other territories in 1130s and in 1143 assisted Toirdelbach Ua Conchobair in the capture of his son Ruaidhrí. In 1144 he was given half of East Meath, with the other half going to Diarmait Mac Murchada, king of Leinster, by Ua Choncobair. Both Ua Ruairc and Mac Murchadh joined the High King in a raid into Munster in 1151. Abduction of Derbforgaill and Norman Invasion of Ireland In 1152, Ua Ruairc's wife, Derbforgaill, was abducted along with her cattle and material wealth by Mac Murchada, who made a hosting into Ua Ruairc's territory aided by Toirdelbach Ua Conchobair. Although the Annals of the Four Masters state that Derbforgaill returned to Ua Ruairc the following year, the matter may not have ended there. In 1166, Mac Murchada was driven from Leinster by Ua Ruairc, Ruaidhrí Ua Conchobair, who had succeeded his father as king of Connacht and High King of Ireland, and Diarmait Ua Mealseachlainn, King of Meath. Despite the fourteen-year gap between Derbforgaill's