Mythical king of Annfwn. Gwynn was the son of Nudd; therefore he was called Gwynn ap Nudd. His father was sometimes called Nudd Llaw Ereint or Nudd the Silver Hand, and identified with the Danann king Nuada Airgetlam. Gwynn's brother was named Edern; he and his brother were named by Culhwch as two of Arthur's warriors.
Gwynn was best known in the tale of Culhwch and Olwen, where he was a rival of Gwythyr fab Greidawl, for the love of Creiddylad. Apparently, Creiddylad was married (or betrothed) to Gwythyr, but Gwynn abducted Creiddylad. Gwythyr pursued, and the two armies fought. Apparently, Gwynn was gaining the upper hand in the war, killing several of Gwythyr's kinsmen and allies.
Arthur needed Gwynn to aid him in the hunt of wild boar, Twrch Trwyth, so he forced a truce between Gwynn and Gwythyr that they would not fight one another in a duel on May Day, each year, until the end of time (or till Judgment Day), while Creiddylad returned to her father to await for the outcome of the duel.
Gwynn and Gwythyr not only took part in the hunt for Twrch Trwyth, they also advised Arthur to send someone else to fight against the Black Hag in the
In the Black Book of Carmarthen, there is a short dialogue between Gwynn and Gwydneu Garanhir. Gwynn has been to Caer Vandwy, a place mentioned in The Spoils of Annwfn. Either Gwynn or Gwydneu witnessed the death of Gwendoleu son of Ceidaw, Bran (son of Gweryd?), Llachau son of Arthur, and Meurig son of Carreian, Gwallawg, and the soldiers of Prydain.
