Described later on as a great warrior with a "blackened face", Gwyn is intimately associated with the otherworld in medieval Welsh literature, and is associated with the international tradition of the Wild Hunt.
Gwyn is the son of Nudd and would thus be grandson to Beli Mawr and nephew of Arianrhod, Llefelys, Penarddun, Afallach, Gofannon, Nynniaw, Peibaw, and Caswallawn.
Gwyn plays a prominent role in the early Arthurian tale Culhwch and Olwen in which he abducts his sister Creiddylad from her betrothed, Gwythyr ap Greidawl.
His skill in combat is extolled in this poem; he is described as "the hope of armies" and "hero of hosts" and, when asked from which region he comes, he simply replies: "I come from battle and conflict.
[4] His role as a psychopomp is paralleled in his later tradition as leader of the Wild Hunt, in which he leads a pack of supernatural hounds known as the Cŵn Annwn to harvest human souls.
"[5] The celebrated fourteenth-century bard Dafydd ap Gwilym refers to Gwyn in a number of texts, suggesting that the character was widely known in Wales during the medieval period.
Some traditions name Gwyn's chief huntsman as Iolo ap Huw, who, every Halloween, "may be found cheering Cŵn Annwn over Cader Idris".
[7] According to a 14th century Latin manuscript against witchcraft, Welsh "dynion hysbys" (soothsayers) would repeat the following:[8] Ad regem Eumenidium, et reginam eius: Gwynn ap Nwdd qui es ultra in silvis pro amore concubine tue permitte nos venire domum.
To the King of the Faeries, and to his Queen: Gwyn ap Nudd thou who art far in the forest for the love of your consort permit us to enter thy dwelling.