Found in the final level of Bastion of Chaos. Sells bad weapons & armor. Also sells potions, various components, and Venomfang Oil Recipe.
DOES NOT ALLOW THE PLAYER TO SELL LOOT.
I have found no real use for him unless you are out of potions.
EDIT: got Relic - Rampage recipe in store on Elite difficulty. Probably he get random recipes to sell sometimes.
EDIT2: got Relic - Sanctuary recipe in store on Normal difficulity
EDIT3 Recipe: Deatwhisper ointment (Elite difficulty)