Piers Polkiss was the best friend of Dudley Dursley and a member of Dudley's gang. Although he did not physically harm the victims of their bullying himself, he held their arms behind their backs whilst Dudley and the others hit them. He, along with the rest of Dudley's gang, chased Harry Potter onto the school roofs, an act for which Harry got into terrible trouble.
On 24 June, 1991, Piers was invited to Dudley's eleventh birthday party, and arrived near the end of breakfast. After a half hour at 4 Privet Drive, they set off for the zoo, laughing as Vernon Dursley yelled at Harry for having a dream about a flying motorbike. He and Dudley were bought large chocolate ice creams and then went to look at the snakes. However, when a boa constrictor escaped from its cage, Piers claimed it had tried to squeeze him to death, and then mentioned how Harry had been talking to it.
Piers was described as a scrawny boy with a rat-like face, although as all of the members of Dudley's gang were described as being large, it is possible he was only scrawny in contrast to the others.