Perfect Peter is one of the main antagonists, if not, a true antagonist of the Horrid Henry franchise. Horrid Henry's little brother, Peter appears to be a perfect and angelic child to the eyes of his parents in contrast to his bratty and rude brother. A wolf in a sheep's clothing, Peter is actually selfish and spoiled by his parents. While keeping this facade, Peter's goals include attempting to bring his brother into trouble even for minor things such as being called a "worm" or told to get "out of my way". Despite this, Peter is occasionally a supporting protagonist of the Horrid Henry franchise.

In many people's eyes like his parents, Peter's image is that of an content, adorable, sweet-natured child that he believes himself to be. His favorite things include fruit and veg, physical exercise, cleanliness, school and books - these factors make people always think the best of him. However, he is in fact another character entirely. He is a condescending and cowardly brat who has a selfish streak for praise and is arrogantly egotistical about it. He is used to getting his own way, and to getting away with everything that he and his brother both do. He also takes an almost sadistic joy in exposing his brother's activities to his parents because it means he gets praised.

He has a weakness that is frequently spurring his doings throughout the franchise: he adores being the centre of attention and becomes intensely furious when this is denied from him. This makes him commit acts that make him just as bad as his brother Henry. He also has an incessant habit of flaunting the smallest things he has done to his parents with the hope of receiving praise - the smallest things, from getting up in the morning to laying the table to polishing his shoes.