In Welsh mythology, Gwyn or Gwynn ap Nudd was the ruler of Annwn (the Underworld). He escorted the souls of the dead there, and led a pack of supernatural hounds, Cwn Annwn.
In the early Arthurian story Culhwch and Olwen, he abducted a maiden called Creiddylad after she eloped with Gwythr ap Greidawl, Gwyn's long-time rival. Gwyn and Gwythr's fight, which began on May Day, represented the contest between summer and winter. He helped Culhwch hunt the boar Twrch Trwyth. Culhwch ac Olwen, translated by Lady Charlotte Guest and sub-edited by Mary Jones. In later legends Gwyn is king of the tylwyth teg or "fair folk".
Gwyn means "fair, bright, white" and is cognate with Irish fionn. Centre for Advanced Welsh and Celtic Studies, University of Wales. "Proto-Celtic—English lexicon." (See also this page for background and disclaimers.). His father, Nudd, is related to the Celtic deity Nodens. J. R. R. Tolkien. 1932. "Reports of the Research Committee of the Society of Antiquaries of London" .The Irish hero Fionn mac Cumhail, whose grandfather was Nuada, is probably related to this figure.
Gwyn ap Nudd is often associated with Celtic goddess Bebhinn, who is apparently his daughter and also the Goddess of Pleasure.