Dictionary of National Biography, 1885-1900/O'Connor, Cathal (d.1010)
O'CONNOR, CATHAL (d. 1010), king of Connaught, was son of Conchobhar, from whom the Ui Conchobhair or O'Connors of Connaught take their name, and was grandson of Tadhg, tenth in descent from Muireadhach Muileathan. From Muireadhach the O'Connors take their tribe-name of Sil or race of Muireadhaigh, and through him they are descended from Eochaidh Muighmheadhoin, king of Ireland in the fourth century. Several of the clan claimed to be kings of Ireland, but no one later than this remote ancestor had any genuine title to the chief kingship of Ireland. The O'Rourkes shared with the O'Connors the alternate sovereignty of Connaught till about the middle of the eleventh century. Cathal became king of Connaught in 980. He built a bridge over the Shannon at Athlone in 1000, and a beautiful doorway at Clonmacnois is attributed to him by Petrie, on the authority of an entry in the registry of Clonmacnois. He entered the monastery of Clonmacnois in 1003, and died in 1010. Five sons survived him: Tadhg an eich ghill, who was king of Connaught from 1015 to 1030, the interval being filled by an O'Rourke; Brian, Conchobhair, Domhnall Dubhshuilech, and Tadhg Direch. His sister was wife of Brian [q. v.], king of Ireland.
[Annala Rioghachta Eireann, ed. O'Donovan, vol. ii.; Petrie's Essay on Ecclesiastical Architecture in Ireland; Annals of Ulster, vol. i. ed. Henessey; Chronicon Scotorum, ed. Henessey.]