‘White’
Gwyn ap Nudd
Originally a Celtic deity, probably of the Otherworld, who appears as one of Arthur’s warriors in Culhwch and Olwen. Gwynn is named as the son of Nudd, and the brother of Edern (Yder) and Owain (Yvain). The son of Nudd, Lord of the Dead of the Underworld (rather than of the Otherworld) and Master of the Wild Hunt. Some sources name his father as Llud Llaw Ereint, in which case he is to be considered as the Welsh equivalent of the Irish Fionn mac Cumhaill.
He loved a lady named Creiddylad (Creiddyledd), and he became enraged when he learned that another warrior named Gwythyr had kidnapped her from the home of her father, Lludd Silver Hand. Gwynn resced Creiddylad from Gwythyr’s fortress and took her to his own home. Gwythyr raised an army to oppose Gwynn. A contest that was ruled should take place every May Day until Doomsday, when the winner would claim the hand of the maiden. The Arthurian cycle adds to the stories of Gwynn ap Nudd, saying that it was Arthur who made the judgement regarding the contest over Creiddylad and that it was also Arthur who made Gwynn ap Nudd Lord of the Dead, ruler over the demons of Annwn, though this combines the Otherworld and the Underworld in an entirely non-Celtic union.
Yet another story says that he was defeated by Saint Tollen (Collen) on Glastonbury Tor, though this fabrication undoubtedly owes its origins to the thought that Glastonbury Tor was a supernatural portal to the Underworld. In folklore, he is said to haunt Glastonbury Tor.
One of Gwynn’s otherwordly castles is suggested to be Caer Vandwy, which Arthur plunders in Preiddeu Annwn.
Source
Culhwch and Olwen | Late 11th century