Ranthru is a mage of the Seers of the Moonstone. The Avatar met him in Ultima Underworld I on the sixth level of the Abyss. Ranthru first asked, if the Avatar was in league with the evil mage Vilus. After getting a negative answer, Ranthru told the story how Vilus turned evil and left for the north-eastern part of the level. They had no idea, if he was still alive (he wasn't). Later, Garamon rescued him when the volcano erupted.