This is Peter Pettigrew. He is the servant of Lord Voldemort. His Amimgus is a rRon's pet rat named Scabbers until be transformed back into a human. He chewed off his own finger to try to prove he was dead, But he just turned into a rat and nobody knew he was a rat. He cut off his own hand to help Voldemort rise to power again, and for him to have his own body and not to share it with someone else.