Two entries with the name Gwenwynwyn.
Gwenwynwyn
Son of Naw and brother of Fflewdwr.
In Culhwch, he is Arthur’s cheif fighter.
Source
Culhwch and Olwen | Late 11th century
Gwenwynwyn
Gwennwynwyn
Son of Naf and brother of Atlandor.
He is one of Arthur’s warriors in Welsh tales, listed as one of the Three Seafarers of the Island of Britain.
He is called “Arthur’s foremost champion” and is the king’s advisor.
Sources
Culhwch and Olwen | Late 11th century
Triads of the Island of Britain (Welsh ”Triads”) | 11th century to 14th century