Peter is not without his character flaws however. He is shown to be very naive, believing his brother's far fetched (and sometimes absurd) stories without question, which often leads him into trouble. He has trouble standing up for himself, and when confronted with brash individuals has a tendency to become a doormat. Peter also seems to relish in being praised, sometimes to the point of being stuck up. He is a constant telltale, and he also enjoys showing off his "perfectness" when Henry gets into trouble (For example, when Mum yells at Henry to get out of bed, Peter would strut by saying "I'm out of bed, Mum!". He also seems to sometimes act perfect towards most people for praise, and despite being called "Perfect" he doesn't always seem to back that up as he can be seen acting cocky towards Henry and even calls him names behind his back. He seem to be accustomed to being praised and noticed by his parents to the point of expecting praise for the simplest deeds, such as using his knife, fork and spoon, not making a mess and "being normal", and would get upset if Mum and Dad do not praise him.
Peter spends his life being dominated and abused by his older brother, Henry, who typically addresses him using derogatory names such as "worm" or "smelly nappy baby", and sometimes even attempts to physically assault him (though this is often, if not always, prevented by their parents). Despite this, Peter appears to look up to his brother, often relying on him to get them out of a bad situation (that the pair are mutually involved in) and even seeks his advice from time to time.
It is hinted that Henry correspondingly secretly feels protective of, and cares for his younger brother. In Perfect Peter Pumps Up, Henry tries to toughen Peter up after being abused by Bossy Bill, Henry's attempt was getting nowhere until he had a idea created by Henry snatching Peter's teddy, Bunny. When Bossy Bill made this fatal mistake, Peter had become fueled with intense anger by Bill's action and taunting words, and when Bill kept pressing his luck, Peter then proceeded to pummel him and later use Bill as a chair in the greatest sense of irony.
In another episode, in which Peter and Henry were locked in the closet, it was revealed that Henry put his life on the line to save Peter from a rather vicious dog when they were younger. Naturally, Henry denies saving him by saying that he wouldn't have cared if that dog had eaten Peter alive, which was an obvious lie. In that same episode, when Peter's life was threatened again by a falling shelf as Peter was trying to get his stuffed bunny, Henry quickly responded with a "NO!" and shoved Peter out of the way. If Henry had not done this, Peter would either be seriously injured or crippled by the falling objects and the entire shelf, thus being in the hospital instead of Henry.
One time, in Horrid Henry, Nothing But The Truth, Peter had said the catchphrase that Henry is usually known for, "Eureka, that's it!" when coming up with a plan to expose Henry for what he truly was.
In Series 4, Peter makes more of a bigger enemy and in episodes like Horrid Henry's Comic Caper and Horrid Henry Gets the Blame and often when Henry plugs in the tablet, Peter unplugs it and Mum accuses Henry for not plugging it in. Sometimes he is a helping hand in the Purple Hand Gang. He is shown to be very sensitive in Horrid Henry Gets the Blame and Horrid Henry's Comic Caper, he cries so that Henry can be blamed.
He also often tells off Henry for even the tiniest thing like not listening to a joke or lifting up his fork and not eating his beans. He is considered a big snitch and in Horrid Henry Eco Warrior he turns into Margaret.
Unlike Henry, Peter has blond hair, with pale skin, a red sweater with a white shirt underneath, grey pants and brown shoes.