Cathal Crobhdearg Ua Conchobair (or Cathal O'Connor / O'Conor) (1153–1224), the youngest son of the Irish High King Tairrdelbach mac Ruaidri Ua Conchobair, was a King of Connacht.
He was King of Connacht from 1189 to 1199, and was re-inaugurated on the stone at Clonalisc.1201, reigning until 1224. He first succeeded his elder half brother Ruaidri's son Conchobar Máenmaige as ruler of Connacht. Conchobar Máenmaige's son Cathal Carrach then ruled from 1199 to 1202, with Cathal Crobhdearg back in power from then. From his base west of the river Shannon he was forced to deal with the Norman invaders. He was a competent leader despite problems, avoiding major conflicts and winning minor skirmishes. Ua Conchobair attempted to make the best of the new situation with Ireland divided between Norman and Gaelic rulers. His long reign was perhaps a sign of relative success. He had succeeded his elder brother Rory O'Connor the previous King of Connacht. He is the subject, as Cáhal Mór of the Wine Red Hand, of the poem A Vision of Connaught in the Thirteenth Century by the 19th-century Irish nationalist James Clarence Mangan.
He founded Ballintubber Abbey in 1216, and was succeeded by his son, Aedh mac Cathal Crobdearg Ua Conchobair. His wife, Mor Ní Briain, was a daughter of King Domnall Mór Ua Briain of Thomond, died in 1218.