Piers Polkiss is Dudley Dursley's best friend. He comes along on the trip to the Zoo and sees Harry talking to the Boa Constrictor - something he lets slip to Vernon Dursley, which earns Harry his longest detention yet.
Piers Polkiss, a scrawny boy with a face like a rat, is Dudley Dursley’s best friend and a fellow bully.
Piers is a member of Dudley's gang. The gang are known bullies; they spend every evening vandalising the play park, smoking on street corners and throwing stones at passing cars and children. When Harry comes across them on Magnolia Road, Piers is congratulating Dudley, or 'Big D', on his right-hook.