What were the two original Japanese Pokémon game versions called?

The two original Japanese versions were Pocket Monsters Red and Green.

Game Freak released them for the Game Boy in Japan on 27 February 1996. As with later paired Pokémon games, the versions contained different obtainable Pokémon, encouraging players to trade in order to complete their collections.

Many international players know the first generation as Pokémon Red and Blue. Japan received an enhanced Blue version later, and that version was reprogrammed as the basis for the international Red and Blue releases. The original Japanese Green version was not released outside Japan in its original form.

This regional difference explains why “Red and Blue” is often remembered as the franchise's first pair even though “Red and Green” came first historically. It is one of the most common early-Pokémon release mix-ups.