Mysterious, immortal being with the power to conjure, control, and resurrect. . . bones! It's almost as though he talks to the bones, softly singing to them, gently coaxing them to do his bidding.
He can even exert some degree of control over the bones of living things too. Although this seems mostly limited to freezing them in place rather than dictating their movements.
Despite his gruesome and macabre powers, Uugathok is not evil. He is more of a nomadic wiseman. Like a wandering, mystic fortune teller for weary adventurers.