Here are the infos and pics of the eight pokemon gym leaders.
Gym Leader no.1
name: Brook
Location: Pewter City Gym
Pokemon Use by him: Geodude, Onix
Best Pokemon to use: Water or Grass
Badge: Boulder Badge
Award: TM34 (Bide)
Gym leader no. 2
Name: Misty
Location: Cerulean City Gym
Pokemon use by her: Staryu and starmie
Best pokemon to use: Electric or Grass
badge: Cascade Badge
Award: TM11 (Bubblebeam)
Gym leader no. 3
name: Lt. Surge
Location: Verlimon City Gym
Pokemon use by him: Pikachu and Raichu
Best Pokemon to use: Ground
badge: Thunder Badge
Award: TM24 (Thubderbolt)
Gym leader no.4
name: Erika
Location: Celadon City Gym
Pokemon use: Victreebell, Tangela and Vileplume
Best Pokemon to use: Fire
badge: Rainbow Badge
Award: TM21 (megadrian)
Gym leader no.5
Name: Sabrina
Location: Saffron City Gym
Pokemon Use: Kababra, Mr. Mime, Venomoth and Alakazam
Best Pokemon to use: Bug or Ghost
Badge: Marsh Badge
Award: TM46 (Psywave)
Gym leader no. 6
name: Koga
Location: Fuchisa City Gym
Pokemon Use: Koffing, Muk, Koffing, weezing
Best Pokemon to use: Fighting or Psyhic
Badge: Soul Badge
Award: TM06 (Toxic)
Gym leader no.7
name: Blaine
Location: Cinnabar Island Gym
Pokemon Use: Growlithe Ponyta, Rapidash, Arcaine
Best Pokemon to use: Water, Ground or Rock
Badge: Volcano badge
Award: TM38 (Fireblast)
Gym leader no. 8
Name: Giovanni
Location: Viridian City Gym
Pokemon use: Rhyhorn, Dugtrio, Nidoqueen, Nidoking, Rhydon
Best Pokemon to use: Water, Grass or Ice
Badge: Earth badge
Award: TM27 (Fissure)