Which pair of Pokémon games introduced the series outside Japan in 1998?

Pokémon Red and Blue introduced the main Pokémon games outside Japan in 1998.

The pair was based on the Japanese Pokémon Red and Green games, which had launched in 1996. For international markets, Nintendo used the updated Japanese Blue version as the technical and visual foundation, while retaining the Red and Blue naming combination. North America received the games in 1998, followed by other regions later.

The original Japanese Green version was not released overseas in its original form. That fact explains why international players often see Red and Blue as the original pair, while Japanese history identifies Red and Green as the first releases.

Both games share the same central story and take place in Kanto, but version-exclusive Pokémon encourage trading between players. Completing the original Pokédex normally requires both versions, along with link-cable trades and, in some cases, special events.