 Before Harry took possession of Bob, he was owned by Justin DuMorne, and before DuMorne, a powerful necromancer by the name of Heinrich Kemmler.According to Jim Butcher, "Etienne the Enchanter picked it (Bob's skull) up on the cheap, back in medieval France, and skulls weren't exactly uncommon.Etienne himself probably had it for the reason that so many writers and sages had skulls hanging around--to make their office look cooler.