 The first Ó Ceallaigh ruler was Aodh Ua Cellaigh, who was killed at the battle of Clontarf, fighting on the side of Brian Boru.His last descendant to rule the kingdom was Feardorcha Ó Cellaigh (died c. 1611).Ó Ceallaigh, O'Kelly and Kelly is one of the most populous surnames in County Galway.