Eliwlad
One of Arthur’s Three Golden-Tongued Knights of the Island of Britain, according to Welsh tradition. Eliwlod was the son of Arthur’s brother Madawg ap Uther, son of (oddly enough) Uther, and thus Arthur’s nephew, although only here is Arthur given a brother.
He appears in a poem known as The Dialogue of Arthur and Eliwlod (Ymddiddan Arthur a’r Eryr). In the poem, Eliwlod’s spirit seems to appear as an eagle to Arthur, perhaps while the latter lies wounded in Avalon, and urges him to accept Christianity. This poem was translated by one Herbert, and Lewis Spence lists among his sources two titles by A. Herbert: Brittania after the Romans and An Essay on the Neo-Druidic Heresy. Beyond this much, I cannot find that Spence throws any further light on the subject, even as to the approximate date of the poem.
It has been suggested that he was the original of Lancelot.
See also
Twenty-Four Knights of Arthur’s Court | The Legend of King Arthur
Source
Triads of the Island of Britain (Welsh ”Triads”) | 11th century to 14th century