Ratbag the Uruk craves power without knowing what he would do with it. He cannot heft a heavy weapon over his head, but he will, stupidly perhaps, attempt to claw his way to the top of Sauron’s Army by aligning with his people’s great enemy, the Gravewalker.
He has deluded himself into believing the Ranger will help him become a Warchief and, once he has power, he will be able to keep all he has achieved. His many scars bear witness to his ineptitude and history of failure. He is a craven little thing whose only chance of success is in spite of himself.