Gralvart, from Ultima Underworld
Gralvart is a mage of the Seers of the Moonstone.
The Avatar met him in Ultima Underworld I on the sixth level of the Abyss. Gralvart acted secretive and asked the Avatar if the hero wanted to have some REAL power. The Avatar said yes, and Gralvart in return explained, how to get a very powerful VAS-Runestone on this level.
The Avatar found it, enabling the hero to cast very powerful spells. Later, Garamon rescued him when the volcano erupted.