Ash Ketchum - The main protagonist of the game, and the only character playable in single player. His Pokémon are Pikachu, Bulbasaur, and Squirtle.
Gary Oak - Ash's rival, and Professor Oak's grandson. His Pokémon are Krabby, Growlithe, and Nidoran♀.
Brock - One of Ash's traveling partners, and Pewter City's Gym Leader, specializing in Rock-type Pokémon. His Pokémon are Vulpix, Geodude, and Zubat.
Misty - One of Ash's traveling partners, and Cerulean City's Gym Leader, specializing in Water-type Pokémon. Her Pokémon are Horsea, Psyduck, and Staryu.
Lt. Surge - Vermilion City's Gym Leader, specializing in Electric-type Pokémon. His Pokémon are Jolteon, Raichu, and Magneton.
Erika - Celadon City's Gym Leader, specializing in Grass-type Pokémon. Her Pokémon are Tangela, Weepinbell, and Gloom.
Koga - Fuchsia City's Gym Leader, specializing in Poison-type Pokémon. His Pokémon are Venomoth, Voltorb, and Golbat.
Sabrina - Saffron City's Gym Leader, specializing in Psychic-type Pokémon. Her Pokémon are Abra, Hypno, and Alakazam.
Blaine - Cinnabar Island's Gym Leader, specializing in Fire-type Pokémon. His Pokémon are Arcanine, Charmeleon, and Magmar.
Tracey Sketchit - Traveled with Ash and Misty through the Orange Islands after Brock chose to stay behind. His Pokémon are Marill, Venonat, and Scyther.
Team Rocket (Jessie, James, and Meowth) - A trio of Pokémon thieves who constantly follow Ash and co. around with the intent of stealing his Pikachu. Their Pokémon are Weezing, Arbok, and Golbat.
Giovanni (unlockable) - The boss of Team Rocket, and Viridian City's Gym Leader, specializing in Ground-type Pokémon. His Pokémon are Sandslash, Persian, and Nidoking.
Ritchie (unlockable) - The trainer whom Ash lost to in the Indigo League tournament. His Pokémon are "Sparky" (Pikachu), "Zippo" (Charmander), and "Happy" (Butterfree).
Lorelei (unlockable) - A member of the Indigo League's Elite Four, who specializes in Ice-type Pokémon. Her Pokémon are Cloyster, Dewgong, and Poliwhirl.
Bruno (unlockable) - A member of the Indigo League's Elite Four, who specializes in Fighting-type Pokémon. His Pokémon are Onix, Hitmonchan, and Primeape.
Mewtwo (unlockable via button code; can only be controlled by Player 2) - A Pokémon created by Team Rocket by cloning a Mew. Its' Pokémon are clones of Pikachu, Bulbasaur, and Squirtle.