Peter Pettigrew
Background
Petter Pettigrew is a former follower of Voldemort. He betrayed the hiding place of his friends Lily Potter and James Potter and set up Lucius Black up for his murder. Peter has secretly been disguised as Ron Weasley's rat Scabbers.
During the events of Harry Potter and the Prisoner of Azkaban (2004) played by Timothy Spall
Harry Potter goes to try and find Peter and Old Man in Portrait tells him to put out his wand light. Peter somehow walks past Harry without Harry seeing him. Later, Scabbers tries to run away and is transformed back into Peter and is caught. As Sirius and Professor Lupin are about to kill Peter, Harry stops them and says Peter needs to be taken to the castle and given to the authorities. They all exit the cavern under the Whomping Willow. Hermione Granger yells out when the full moon starts to peak over the horizon. Lupin starts to change into a werewolf and Peter manages to escape.