A Persian warrior assigned to champion Persia against Rome in a dispute over Jerusalem. For its champion, Rome presented a young Gawain (not yet in the service of Arthur).
Gawain, although young and strong, seemed little match for the gigantic, courageous, and experienced Gormundus; however, after a battle that lasted three days, Gawain delivered a mighty blow to Gormundus’s head, killing him.
Source
De Ortu Waluuanii Nepotis Arturi | Late 13th century