The Vark originally worked with the old gods to prepare Kaelus for their children. Some believe that the Vark were the old gods first attempt at children while other theories claim the Vark were part of Kaelus, like the rocks or the ocean. Whatever you believe all the Vark were destroyed by the old gods at the end of the Long War.
What the Vark looked like can only be ascertained from sculptures and artist renditions
Post Betrayal Vark