Anthony lives in the Hoenn region near Rustboro City where he ran an unofficial Gym with what he called the world's strongest Pokémon. He put up a big sign so that passing trainers would come and battle him. Unfortunately for these trainers, they didn't know that he cheated during Pokemon battles by having several other Pokémon ride inside his Pelipper's mouth.
It wasn't until a battle with
Ash Ketchum that things started to go wrong for him and the battle between
Ash's Pikachu and
Anthony's Pelipper ended in a draw. Team Rocket actually found out about his scheme and blackmailed him to cooperate with them otherwise they'd tell the world and it would stain the legend of the world's strongest Pokémon.
Anthony had a change of heart after his Pelipper was returned to his care after Team Rocket was defeated and Anthony pledged to actually raise it to be the world's strongest.