Galleghar and the Thief share powers. I don’t know how or when or why the two of them linked up, but I would stake serious money on the two being co-bound. That would explain why Galleghar keeps popping up during our search for the Thief. He’s hooked on the same magical power line that the Thief of Souls is. So long as their magic is bound together, you can’t have one without the other.