Recorded as Mac Cuolahan, O' Cuolahan, Cuolahan, Coolahan, Coolican and others, this is an Irish surname of great antiquity. It derives from the medieval Gaelic Mac Culachain or O' Culchain, both in effect meaning the male descendant of the proud one. Who the "proud one" was is unclear, but the great majority of Irish surnames do originate from a nickname for the first chief of the clan. The Mac name is often confused with Mac Coughlan mainly because in the past the Mac Cuolahans and the Mac Coughlans shared ownership of the parish of Lusmagh in the barony of Garrycastle, County Offally. The Mac Cuolahans were also known as the lords of Sil Anmchadha in County Galway, and later the Mac prefix was changed to O' by incorrect useage. It seems as well that in the 17th century the clan occupied the village of Ballymaccoulighan, which is logical, whilst in 1690 Daniel Cuolaghan was a lieutenant in the army of King James 11nd, defeated at the battle of the Boyne. It is said that the original O' Cuolahans were from Carra in County Mayo, with Diarmid O' Culachain being a professor of history at Knock in 1221.