Chopper is a member of the Cycling Road bike gang, a group of territorial riders who challenge trainers crossing their bridge. He's best known from the episode "The Bridge Bike Gang."
Before joining the gang, Chopper and fellow biker Tyra were actually close with Jessie and James—the two left the biker life to pursue their Team Rocket careers instead.
When Ash rolled through, Chopper challenged him to a battle. His Golem managed to take down Ash's Bulbasaur, but lost to Charmander. Later, the gang tried to stop Ash and friends again as they rushed across the bridge in bad weather to deliver medicine to a sick Shellder. Ash refused to fight, explaining the urgency of his mission. That's what won Chopper over—he was genuinely impressed by Ash's willingness to risk himself for a Pokémon's sake. He and the other bikers actually escorted the group to the nearest Pokémon Center and even gave Ash the honorary title "Awesome Ash" for his dedication.
Content compiled by AnimeList.moe from publicly available sources.
