Which main-series Pokémon games first introduced Double Battles?

Pokémon Ruby and Sapphire first introduced Double Battles in the main Pokémon series.

Released for the Game Boy Advance in Japan in 2002, Ruby and Sapphire expanded battles from one Pokémon on each side to two Pokémon on each side. This created new strategic possibilities, including attacks that affect multiple targets, moves that protect an ally, and combinations involving abilities or weather.

Double Battles became part of the wider Pokémon battle system rather than a one-time experiment. They appear in certain Trainer encounters, official competitions, and later games. Players must consider targeting, positioning, team synergy, and the possibility that an attack may also affect a partner.

The format is different from ordinary single battles, which remain the standard battle type for much of the series. Pokémon Stadium and other earlier spin-offs had their own battle rules, so Ruby and Sapphire are specifically credited with introducing Double Battles to the main-series games.