According to the Prose Tristan, the large son of Duke Frollo of Germany who went on to become a knight of great renown.
Although he was knighted by Galahad, he opposed Arthur’s knights for having defeated his father. During the Grail Quest, he fought and defeated Kay, Gaheris, and Girflet.
See also
Gauna | The Legend of King Arthur
Source
Post-Vulgate Queste del Saint Graal | 1230-1240