Final answer:
The Pewter City Gym Leader in the Pokémon series is Brock, who specializes in Rock-type Pokémon and offers the Boulder Badge to trainers who defeat him.
Step-by-step explanation:
The Pewter City Gym Leader in the Pokémon series is named Brock. He specializes in Rock-type Pokémon and is known for his defensive battle tactics. Trainers seeking to earn the Boulder Badge must defeat him in battle. Brock is not only a Gym Leader but also has aspirations of being a great Pokémon Breeder.