i think its in fuchsia city.
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Brock.
He is the Gym Leader in Cinawood.
in blackthorn city
you beat the last gym leader in johnto
you have to beat the last gym leader
You CAN NOT become a Gym Leader in Pokemon HeartGold and SoulSilver or ANY MAIN SERIES POKEMON GAME.
Not enough info: which gym leader?
The thirteenth gym leader is Janine. She is filling in for her dad, Koga. She uses poison type Pokmeon. Make sure to bring a ground Pokemon for an easy battle.
In the goldenrod gym.
Brock.
beat gym leader
in seafoam island
defeat gym leader.
Jeff Gordon
in blackthorn city
He is the Gym Leader in Cinawood.
Simply beat the gym leader in every gym.