Petre, variously known as Peter, Pierrot, or Piero, originates as a mallard duck character. Initially presented as a bully duckling in early media, he frequently targets Calimero with mean pranks, acting as an antagonist figure, often aided by his piglet sidekick Buta. In the 1974 series, he continues this troublesome role, interfering in Calimero's life, including interactions with Priscilla, consistently acting as an obstacle.

A character shift occurs in the 1992 series, transitioning him from antagonist to ally. He becomes Calimero's friend, joining an investigation team with Priscilla to solve mysteries. This series also introduces his romantic relationship with Susie, a bespectacled girl duck. The progression continues in the 2014 CGI series, where he is fully integrated into Calimero's friend group. Now referred to as Pierrot in some dubs, he participates in daily adventures as a regular companion. He explores the Mill—a hideout featuring inventions by Calimero's ancestor—alongside Calimero, Priscilla, Giuliano, and others, visually distinguished by a pink scarf and blue jacket.

Throughout adaptations, his background as a duck remains consistent, his narrative trajectory evolving from antagonism to friendship, cementing his role within the core group's social dynamics.