The descendants of King Brian Boru were known as the Uí Briain (O'Brien) clan, hence the surnames Ó Briain, O'Brien, O'Brian etc. O was originally Ó which in turn came from Ua, which means 'grandson or descendant' (of a named person). TheO'Brien Clanare ranked as one of the chiefdynasticfamilies of Ireland.
