Koga's Pokemon are:
Koffing
Muk
Koffing
Weezing
no
Giovanni
saffron city (psychic type gym leader)
The 7th leader is Blaine. He uses fire pokemon.
water or grass type Pokemon
charizard
You go to saffron city
no
The fifth Gym can be found in Fuchsia City. The leader is Koga, who specialises with Poison-type Pokémon.
The Gym Leader that allows you to use the HM move Strength in Pokemon FireRed is Erika. Erika is the Gym Leader of Celadon City and is the 4th Gym Leader the player faces.
beat the gym leader
Giovanni
saffron city (psychic type gym leader)
there is no gym leader in lavender town
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The 7th leader is Blaine. He uses fire pokemon.
You cannot be a gym leader yourself in any of the Pokemon games, so far.