An enchanter, son of Collurery, in Welsh legend who studied under Gwythelyn the Dwarf (Grudlwyn Gorr).
He was said to have tended the magical pig Henwen, which gave him the designation of one of the “powerful swineherds of Britain”. His name is attached to Arthur’s in a revised Welsh Triad, in which Arthur tries to hunt down and kill Henwen.
He is otherwise non-Arthurian, but his name was used by some Middle-English romance writers, including Chaucer.
Source
Triads of the Island of Britain (Welsh ”Triads”) | 11th century to 14th century