Philip Chang sent his son into hiding while he was still an infant. Born in Hong Kong but raised in Seattle, Percival Edmund soon became known as "Grunge", an all-American slacker who knew little about his brave father. He was eventually invited to take part in I.O.'s Project Genesis, where Grunge soon found out he was in a prison-like breeding ground for Gen-Actives. Manifesting his powers, he escaped with his new teammates, a group soon to be called Gen¹³. They take a temporary break and Grunge travels with Freefall to Las Vegas, where he gets into trouble due to a high win rate. His abilities make it seem as if he and Freefall were statues.
Grunge is a skater/surfer and enjoys spending his afternoons sleeping in. Only Freefall appreciates him for who he really is. However this never stops Grunge from trying to hit on Caitlin Fairchild constantly, in many maneuvers that sometimes violate her right to privacy. Freefall initially goes unnoticed, despite her feelings for him and Rainmaker attempts to serve as the voice of reason for Grunge's attitude, going roundly ignored. Only after a weird episode involving a demonic entity attempting to consume his soul via a rare collector's comic edition, and Grunge's resulting dream in which he meets several characters from external comics series (Archie Andrews and his friends, the Teenage Mutant Ninja Turtles, Fone Bone and Spawn), does he realize both Roxie's and his own feelings for each other, and they begin a romantic relationship.
Despite his personal history, Grunge is dependable on the battlefield, listening to orders when given and improvising new ways to help. His sound system defeated the villain known as Helmut. When the girls were kidnapped by a toy manufacturer, Grunge used the properties of the toys themselves to help rescue them. After a notable round of cluelessness, Grunge travels to the desert alone and confronts a trickster deity who puts him through his paces. He is picked up by his friends, who believe he was just hallucinating everything because he did not bring enough water.
The interruption to regular life brought on by super-powers is normalized a bit when Grunge returns to school. He ends up with Caitlin in high level classes due to his photographic memory. His poor choice in new friends almost leads to the loss of old ones, as they do not like Rainmaker's more peaceful worldviews. It does lead to the release of an angry, super-strong simian that had been experimented upon in the school's laboratories.
Grunge's life is interrupted when I.O. forces blow up his house and slay the robotic housemaid. Grunge and friends travel to a small island where Lynch's friend is operating. Unfortunately the island contains a spaceship, which takes Grunge and Caitlin deep into space. There, he is affected by an alien system and goes on a rampage.
Grunge's second trip into space was not so far, only going so far as the moon in order to help out in the Fire and Heaven incident.
Appearances in other media
In the Gen¹³ animated movie, Grunge's voice was provided by Michael Balzary, better known as Flea from the rock band The Red Hot Chili Peppers.