Cormac mac Art Ó Melaghlain, was King of Mide from about 1205 to 1239. He was acknowledged as one of the most ferocious and formidable opponents of the Normans since their arrival in Ireland. He died at Inisdowginn on the river Suck, near Dunlo in Hy-Many, in 1239.
Cormac was born sometime in the early 1180s to the King of Mide, Art mac Mael Sechlainn meic Domnaill Ua Mael Sechlainn, who reigned from 1173 to 1184. His family had been rulers of the Kingdom of Mide since at least the early 6th century. Initially known as the Clann Cholmáin, they were a branch of the southern Uí Néill. They had taken the surname Ua Mael Sechlainn after their prestigious ancestor, Máel Sechnaill mac Maíl Ruanaid, who reigned as High King of Ireland from 845 to 860; his greatest achievement was in preventing the Vikings from controlling any substantial part of the island and confining them to the coasts. One of his descendants, and another of Cormac's ancestors, was Máel Sechnaill mac Domnaill Ua Maelsechlainn (known as Máel Sechnaill II) who was High King before and after the reign of Brian Boru.
Yet from the death of Máel Sechnaill II in 1022 the rulers of Mide had lost much of their previous strength and authority to rival dynasties such as the O Briens (Kings of Munster), the O Conchobhars (Kings of Connacht) and the Mac Murchadhs of Uí Cheinnselaigh (Kings of Leinster). Despite, or perhaps because of, its situation in central Ireland, Mide found itself being used as a pawn in the power-struggles of the newly-dominant kingdoms, as real power on the island shifted to the previously marginalised dynasties of Leinster, Munster and Connacht. Caught between these three super-powers, in addition to predation from their northern kinsmen, the Kings of Ailech, it became a matter of survival to become an ally of one or be seized by all. Therefore, during the long reign (1119–1156) of Tairrdelbach mac Ruaidri Ua Conchobair, Mide was annexed by Connacht.