Culhwch and Olwen includes Edern son of Nudd among Arthur's companions, next to Gwyn ap Nudd. Their patronymic and the pairing suggest a brotherly relationship, although the brief notice does not tell a story about their childhood or establish Edern as a god. Wider comparisons involving Nudd, Lludd and other figures belong to the interpretation of Welsh mythology. They should not be used to assemble an unquestionable divine family tree. Edern enters this tale as a member of Arthur's remarkable company, not as the hero of a separately narrated adventure.

His fullest familiar Welsh episode begins when a knight's dwarf strikes Guinevere's attendant and then Geraint. Unable to answer properly while unarmed, Geraint follows the party. He finds lodging with the impoverished Earl Ynywl and meets Enid, whose beauty becomes central to the contest ahead. A sparrowhawk is offered as the prize in a challenge involving the knights' ladies. Edern is the established champion whom Geraint confronts. The hawk's role is that of a contested prize, not evidence that Edern habitually rides with it on his wrist.

After a prolonged combat, the defeated knight names himself Edern son of Nudd. Geraint requires him to go to Arthur's court with his companion and dwarf and answer for the earlier insult. Guinevere is not standing at the battlefield to plead for his life. At court she hears his account, and Arthur's household arranges mercy, guarantees and treatment for his wounds. Edern later accompanies Geraint among the company travelling towards Cornwall. The story therefore moves beyond defeat to his reintegration among Arthur's people, rather than ending with a nameless enemy discarded after the tournament.

The Dream of Rhonabwy places Edern in a different literary setting. He leads the men of Denmark, whose black garments have white borders, and appears among Arthur's counsellors. The elaborate colours belong to the dream's visual description; they do not describe troops whose bodies are divided into white and black halves. Geoffrey of Monmouth also includes a Hiderus son of Nu in Arthur's continental war, and Wace uses the related name Yder. These correspondences reveal the circulation of the character's name without requiring every writer to preserve identical origins, titles or deeds.

Other traditions broaden the picture. The French Yder becomes the subject of a romance, while the Modena carving labelled Isdernus is associated with this knight in discussions of early Arthurian imagery. Its interpretation should not be turned into proof that every later story had already existed unchanged. A Brent Knoll giant-fighting episode appears in an interpolation in the Glastonbury history attributed to William of Malmesbury, not simply in a securely dated original passage by William himself. Welsh dedications to a saint Edern, meanwhile, include a figure with a different patronymic, Edern ap Beli. Distinguishing that saint from Edern fab Nudd preserves the knight's literary identity without treating every occurrence of the name as one life.