Campbell is a Scottish surname, one of the ten most numerous in that country, and one of the thirty most numerous in Ireland, with over two-thirds of those who bear the name living in Ulster. It is particularly common in counties Armagh, Down and Antrim. Originally a nickname, it comes from the Scots Gaelic cam beul, meaning "crooked mouth".
Clan Campbell was founded by Gillespic Ó Duibhne, who lived in the thirteenth century, and was the first to assume the surname. His descendants included the most famous branch, the Campbells of Argyll, one of whose members was responsible for the massacre of McDonalds of Glencoe which led to the famous feud between the two clans.
The vast majority of Irish Campbells are descended from the Scottish family, although in Co. Tyrone, the surname may be an anglicisation of the Irish Mac Cathmhaoil, from Cathmhaol, meaning "battle-champion".