Cormac Mac Airt (son of Art), also known as Cormac ua Cuinn (grandson of Conn) and Cormac Ulfada (Long Beard), King of Ireland. He was son of King Art the Lonely and grandson of Conn of the Hundred Battles.
Cormac became king of Ireland in 218 and reigned until 254, when he handed the throne to his son, Cairbre Liffeachair. His abdication was prompted by blindness in one eye, caused by the same poison spear which killed his son Cellach. He retired to Aicill (hill of Screen) and turned his energies to the writing of laws. The Brehon Laws were thought to have been drafted by or under the patronage of the literate Cormac Mac Airt.
It was King Cormac who commissioned to build the first mill in Ireland, but his reign is remembered most because of the career of the legendary warrior Finn MacCumhail and the deeds of the Fianna.
Cormac owned the wonderful gold cup given to him by the sea-god Manannan mac Lir in the Land of the Living. If three lies were spoken over it, it would break in three; three truths made it whole again. Cormac used this cup during his kingship to distinguish falsehood from truth. When Cormac died, the cup vanished, just as Manannan had predicted it would.
Cormac is said to have turned to Christianity some years before his death. One account of his death says he choked on a fish bone, but according to Lebar na h-Uidhre, he was killed by the siabhra, or fairy beings, for abandoning the old religion. Cormac died at Cleaiteach in 260. It is said in ‘Lebar na h-Uidhre’ that he desired to be buried at Ros na righ, but after his death it was decided that he should be interred at Brugh na Boinne, ‘where all the kings of Tara were buried.’ When, however, they proceeded to carry out their purpose, the river Boyne ‘rose against them three times,’ and they had to abandon the attempt, and he was taken to Ros na righ, which was thenceforward the burial-place of the Christian kings. The reign of Cormac is the epoch at which most of the monuments remaining at Tara had their origin.