Brian Boru

Brian Bóruma, known as Brian Boru (c. 941–23 April 1014), made himself king of Munster by 978, then subdued Dublin, Leinster and the northern Uí Néill. In 1002 his rival acknowledged him high king of Ireland, ending the Uí Néill hold on the high kingship.

In 1014 his army met the Norsemen of Dublin and their Leinster allies at Clontarf: Brian's forces won, but the elderly king was killed. He founded the O'Brien dynasty.