In the Pokémon anime, Brock was the first Kanto Gym Leader Ash defeated. Brock led the Pewter City Gym and specialized in Rock-type Pokémon, making him Ash’s first official Gym challenge after leaving Pallet Town.
Their battle was unusual. Ash’s Pikachu struggled against Brock’s Geodude and Onix, but the battle was interrupted when the Gym’s sprinkler system activated. Pikachu’s electric attack then helped Ash overcome Onix. Although Brock believed the interruption meant Ash had not truly won, he awarded Ash the Boulder Badge after recognizing Ash’s determination and concern for his Pokémon.
Brock did more than hand over Ash’s first badge: he soon left Pewter City to pursue his dream of becoming a Pokémon Breeder and joined Ash’s journey. This is why viewers often remember Brock as both Ash’s first major Gym opponent and one of his longest-running companions. Misty was the next Kanto Gym Leader Ash challenged, at the Cerulean Gym.