A knight slain by Gawaine in Heinrich von dem Türlin’s Diu Crône.
He inhabited an enchanted castle in the land of Sere, from which Gawaine had to retrieve a bridle. Berhardis was cursed to decapitate any challengers.
After Berhardis’s death, Gawaine discovered that both the castle and the knight were part of his own territory, acquired by his marriage to the lady Amurfina (Amurfine).
Source
Diu Crône | Heinrich von dem Türlin, c. 1240