Simplify the following text for a Grade 8 native English-speaking person.
Original: Brock is the Gym Leader of Pewter City in the fictional region of Kanto . He specializes in Rock-type PokÃ mon , and the player may battle him in PokÃ mon Red , Blue , Yellow , Gold , Silver , Crystal , FireRed , LeafGreen , HeartGold , SoulSilver , and PokÃ mon Stadium .
Simplified: Brock appears in the game PokÃ mon Red and Blue and its remake FireRed and LeafGreen as the gym leader of Pewter City .