He is a golden Bidoof.
Peanut Butter is loyal to his 'Father', Rusty. It is implied that he killed nearly every Pokemon Trainer holding a badge, and has killed Agatha on Screen. After learning 'Vengeance for Mankind', he enslaved the world under the impression that all human beings are evil. He learned from Good Rusty, that there is good in the world, and now seems compassionate.
Perfect Bidoof returned in "Jailbreak", calling Rusty his father from when he (and Julian) had created him. He rescued Rusty from being kicked in the taint and killed by Wet Craig ordered by Shady Dan. Rusty nicknamed him "Peanut Butter."
In "The Elite Four", Peanut Butter teleported as Rusty called him. He carried a sack full of trainers' badges, covered in blood. Rusty didn't know what happened because Peanut Butter told him to cover his eyes in every trainer battle. As Rusty used Burbasaur to fight against the Elite Four member Agatha and her Gengar, Peanut Butter tells Burbasaur to rest because Burbasaur cannot fight due to organ failure. He cast a spell onto Agatha, causing Bidoofs to come out of her eyes and mouth to her excruciating death. After the incident, the remaining members fearfully congratulated Rusty as new Elite Four member. Peanut Butter teleported with Rusty to McDewgong's to eat some food.
In " Legendaries", they arrive at the nature reserve where the see Suicune. Rusty then asked Peanut Butter to use one of his moves, but Peanut Butter then proceeds to disintergrate suicune. Shortly after, the tour bus arrives and invites Rusty and Peanut Butter to join them. During the tour they are shown various legendary Pokémon until they arrive to see Arceus. Then a poacher arrives to kill him. Peanut Butter realizes his true purpose and then informs Rusty he has learned compassion but already has four moves. Rusty then tells him to forget compassion to which he promptly does and then informs him that he learned another move thirst for vengeance Rusty agrees to let him learn the move. Peanut Butter then kills the hunter and proclaims the age of man is over and for his companions, other pokemon, sake he wouldn't serve humans but instead rule them. Rusty says that he will do that by doing everything Rusty says.
Six Months Later, Rusty and several slaves are seen building a statue of Peanut Butter with giant muscles and after singing, Rusty is lashed and falls to the ground form a ledge to work on. Rusty is rescued by Battle Bart and brought inside a hideout where he has to rewind time so he doesn't create peanut butter. he is also told that Red brought a bunch of trainers to fight peanut butter but they were killed by his magic. After he comes back EV Trainer questions what happened while a red laser cuts through a wall behind him. The wall then explodes with Ev Trainer falling to the ground bleeding and peanut butter coming out of the hole in the wall. He then gets prepared to fight Rusty who throws pokeballs at him and fails. In the Final Episode, Peanut Butter prepares to kill all of humanity. Rusty attempts to stop him again by throwing a Pokeball and once again failing. Just before, Peanut Butter kills Rusty and the rest of his team, Deli Rusty arrives with the sandwich ordered by Battle Bart. Here Peanut Butter eats the sandwich and has a new found hope in discovery. He then takes Deli Rusty and Sexy Clefairy to space to explore the wonders of the universe leaving normal Rusty behind to forever work in the Deli.
Six months later in "Bidocalypse", Peanut Butter discovered the secret hideout for Anti-Bidoof Resistance using red laser. He prepared to finish off the remaining members. As Rusty failed to use his Pokeball to capture him, he retaliated by transforming Julian into Bidoof and exploded him, and he also transformed Professor Tree who makes his last will for Rusty.