Gawain’s foster-father, a poor but nobly-born fisherman living near the city of Narbonne in Gaul.
Gawain’s mother had given Gawain, as a baby, to some merchants, who docked their ship and left it unattended near Viamundus’s home. Viamundus came across the ship, found the infant and a pile of unguarded wealth within, and helped himself to both. Finding no way to spend his ill-gotten gains without arousing suspicion, Viamundus eventually journeyed to Rome with the spoils, representing himself as a noble Roman warlord from Gaul.
The ruse worked, and the Roman Emperor awarded Viamundus a manor with in the city, where he lived out his days in relative luxury, raising Gawain to be an honorable and skillful knight. On his deathbed, he repented to the Emperor and to Pope Sulpicius, confessing his crime and deception. The Emperor, who had been his friend, forgave him and buried him in a tomb among the other Roman nobles.
See also
Gawain the Brown | The Legend of King Arthur
Source
De Ortu Waluuanii Nepotis Arturi | Late 13th century