Thymbrak is an adventurer you can find in the Goblinclaw Inn, and will be the guideline for several quests (see Dreadstone for them). He is only available there through the early stages of the Dreadstone Saga, so if you want to trade with him (see below), do it ASAP.
He's supposed to be a formidable adventurer, and lets you look at some of his items, which you can't aquire:
Three powerful enchantments were long ago bestowed upon this magnificent chain shirt. It is believed that the wearer of this piece of armour is immune to the effects of a dragon's breath and all magical fire.