Tighearnán Ua Ruairc, anglicized as Tiernan O'Rourke (d.1172) was king of Bréifne, an area encompassing the modern diocese of Kilmore in Ireland, and including the area which in later times became known as (West Brefney, or Brefney O'Rourke the modern county of Leitrim) from c. 1124 onwards. He was one of the most successful and ruthless 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 of Connacht.
His wife, Derbforgaill, gained him notoriety as the most famous cuckold in Irish history, when she was abducted by Diarmait Mac Murchada in 1152, although Tigernán did eventually, in 1167, extract legal recompense from Diarmait for this insult to his honour.
Tighearnán had three children, Melaghlin, Aed and Dowchawley, all of whom predeceased him. He was also probably the foster-father of Brian Bréifneach Ua Conchobair, son of Toirdelbach, who was blinded by his own brother Ruaidri Ua Conchobair to disqualify him from fighting for the kingship after their father's death. Tighearnán as usual had a foot in both camps: his daughter Dowchawley was Ruaidri's wife.
Tighearnán has gone down in history as a violent and treacherous character. The Annals of Ulster record in 1128 his robbing and killing of some of the Archbishop of Armagh's company, calling it 'A detestable and unprecedented deed of evil consequence'.
Giraldus Cambrensis had even less time for him, describing his death at the Hill of Ward in Meath during negotiations with Hugh de Lacy as all part of a treacherous plan gone wrong. His head was sent to Henry II, while his body was hung upside-down outside Dublin Castle. There was probably double dealing on both sides, as the Irish annalists record the incident as showing the duplicity of the English.