Brian Boru was a powerful Irish king who ruled in the 10th and 11th centuries. He is best known for his victory at the Battle of Clontarf in 1014, where he defeated the forces of the King of Leinster and the Viking invaders. This battle is often seen as a turning point in Irish history, as it marked the decline of Viking influence in Ireland. Brian Boru is also remembered for his efforts to unite the various Irish kingdoms under his rule, and he is considered one of the most important figures in Irish history.