Gurstang, from Ultima Underworld
The Avatar learned from the mage Illomo on the sixth level of the Abyss in Ultima Underworld I that on their search for the Key of Truth, Gurstang had been lost on the seventh level, never to be heard from again. The Avatar freed him from Tyball's prison on the seventh level of the Abyss after slaying the evil mage.
Gurstang had already felt Tyball's death, and when the Avatar mentioned Illomo, Gurstang told the hero to give Illomo the good news of his newfound freedom, and to tell him the password "Folanae", which would be vital to find the Key of Truth.
Later, Garamon rescued him when the volcano erupted.