Often described as a pudgy boy, Peter was never far from the other three troublemakers in his group.
By comparison, Peter was extremely unpopular but a somewhat valued member of the group, receiving the nickname 'Wormtail' after his form as an animagus.
Peter may have gone on to perform some horrible acts, constantly seeking the most powerful figure he could to hide behind, ironic for someone who was supposed to value bravery. Then again, he likely idolised the other three for their bravery.. it doesn't explain why his next master was lord voldemort himself however...
There are many stories of the life of Peter Pettigrew, enjoy the snippets that follow.