Cei was among the party assembled by Culhwch in his quest to locate the maiden Olwen, a story told in the Mabinogion story of Culhwch and Olwen. Cynyr Fair Beard is given as Cai's father in Culhwch. He is one of Arthur's chief warriors, together with Bedwyr, in the arthurian traditions. He is said have a sharp tounge and quick temper.
Each of the party was chosen for a particular skill or attribute. Cei's talents were his ability to stay for nine days and nights without breathing or sleeping and to change his height at will. In addition, his body temperature was so high that he never got wet, and during the cold his companions could kindle a fire from him.
Witches and witchcraft | Myths and Legends