Topuru, from Savage Empire
Topuru used to be a powerful shaman, challenging other shaman to combat, but after an encounter with Balakai of the Barrab Tribe, he quite literally believed he lost his mind. After losing his mind, his apprentice Wamap kicked him from the tribe, and now he lived alone on a small island. Topuru would not tell the Avatar the location of the Urali tribe until his mind was restored.
After restoring Topuru's mind, Topuru told the Avatar about the secret entrance to the Urali village, and gave him turtle food, which could be used to summon a rideable turtle in swamplands.