Brian Boru (941 - April 23rd, 1014) was the first, and only, Emperor of Ireland. A clan prince, he first subjugated Munster and then extended his power over all of southern Ireland. By 1002 AD he had subjugated most of the kingdoms of Ireland.
Ruling from 1002 to 1014, he came into conflict with the Norse inhabitants who formed a coalition against him. Brian defeated them at the Battle of Clontarf, but he was murdered in his tent shortly thereafter. Brian's victory had broke the Norse power in Ireland forever, but his untimely death plunged Ireland into anarchy.