Thalzar was one of a trio of wizards to escape Crandor after Elvarg laid waste to the island. He, Lozar and Melzar (of whom Melzar is the last survivor, later to be killed by the adventurer) each took a piece of the Crandor map, in the hope of preventing others from journeying there. It is assumed Thalzar died peacefully; his third of the map is found in a sealed room in the Dwarven Mine, and the Oracle is now charged with ensuring only those strong enough to defeat Elvarg are given access to Thalzar's map piece.
Thalzar's message (click to enlarge)
During the Dragon Slayer quest, players will encounter an engraving from Thalzar on the lid of the chest containing one of the map pieces. It makes brief mention of the events on Crandor and asks the player to reconsider taking the map piece within.