Son of Constantine and father of Arthur’s warriors Geraint, Ermid, and Dywel.
Erbin ruled a Cornish kingdom, which he had to turn over to his son Geraint when he became ill. Geraint returned rule of the land briefly to Erbin when Geraint left for a series of adventures, but he eventually came back and took the crown from his aging and grateful father.
His counterpart in the French romances, as Erec’s father, is Lac.
Source
Culhwch and Olwen | Late 11th century
Geraint and Enid | 13th century