In Goidelic Celtic mythology, Cormac mac Airt was the son of Achtan and Airt. He may have been a historical Irish king. He ruled from Tara, the capital of the High Kings of Ireland for forty years, probably AD 227 to 266.
The sea god Manannan Mac Lir[?] gave him a magical gold goblet. It would break into three pieces when three lies were told over it; speaking three truths would fix it.