Diarmait Ua Briain

Diarmait Ua Briain (c. 1060–1118) was a son of Toirdelbach Ua Briain, king of Munster. After their father died in 1086 his brother Muirchertach drove him into exile, and he is thought to have led an Irish fleet to victory at the Battle of Mynydd Carn.

Reconciled in 1093, he ruled Waterford, and in 1114 took the kingship of Munster when Muirchertach fell ill, triggering four years of civil war. He died at Cork in 1118, after which Toirdelbach Ua Conchobair invaded and partitioned Munster.