Pokémon Red and Blue were the international releases based on Japan’s original Pokémon Red and Green games.
In Japan, Pocket Monsters Red and Green launched for the Game Boy in 1996. Nintendo and Game Freak used the updated Japanese Blue version as the technical and visual basis for the international editions, then released those games overseas as Pokémon Red and Blue. The original Japanese Green version was not released internationally in its original form.
The games preserve the first-generation setting, mechanics, and 151-species Pokédex while presenting revised artwork, scripts, and other adjustments. Their version-exclusive Pokémon also retained the series’ trading-based design, encouraging players with different cartridges to exchange creatures.
Pokémon Yellow was released later as an enhanced version inspired partly by the anime, with Pikachu as the player’s initial partner. FireRed and LeafGreen were much later remakes for the Game Boy Advance, so neither is the original international counterpart.