Which Game Boy games launched the Pokémon series in Japan?

Pocket Monsters Red and Green launched the Pokémon series in Japan on the Game Boy.

The paired role-playing games introduced the basic Pokémon formula: exploring a region, capturing creatures, training them, battling other Trainers, and trading with another player. Their setting was the region later known internationally as Kanto, and their Pokédex contained the original 151 species.

Japan received Red and Green rather than the Red and Blue pairing familiar to many international players. Nintendo later released an enhanced Blue version in Japan, and the international editions were based on that revised version. Outside Japan, the games became known as Pokémon Red and Blue.

Pokémon Yellow followed in Japan as an enhanced title featuring Pikachu more prominently. It is therefore not the series debut, even though it became many players’ first Pokémon game. The original Red and Green release established the Game Boy series that grew into a major Nintendo franchise.