After Ash Ketchum loses to Brock, a stranger (Brock's father) offers to help make his Pikachu stronger. Pikachu becomes strronger and manages to defeat Geodude, but Onix remains too strong. Onix has Pikachu in a body bind;
Since then, he travels with Ash Ketchum and Misty on his many adventures. In the Orange Islands series, he leaves the team to join Professor Felina Ivy, but mysteriously returns to Pallot Town when Ash Ketchum wins the Orange League Championship.
By defeating his mother, he restores the Gym's reputation, and proceeds to leave all his Pokemon (Except Forretress) to his younger brother Forrest, before departing for the Hoenn region, where he catches up with Ash Ketchum and his two new friends, May and Max. The group travel across Hoenn and then return to Kanto to participate in the Battle Frontier. The group went their separate ways and Brock met up with Ash Ketchum in Sinnoth. They met a new coordinator named Dawn (Pokémon) and their partner Piplup, who joins them on their journey through Sinnoth.
During this time, both Brock's father, Flint (who was also Brock's predecessor as Gym Leader (Pokemon)), ran offf again, and his oldest younger brother Forrest took the role of Gym Leader (Pokemon) in Pewter City, as well as the responsibility of caring for his many younger siblings. Brock is the oldest of ten siblings, with five brothers and four sisters.