Which Pokémon games introduced the Abilities mechanic?

Pokémon Ruby and Sapphire introduced the Abilities mechanic.

Released for the Game Boy Advance in Japan in 2002 and internationally in 2003, Ruby and Sapphire began the third generation of Pokémon games. Each Pokémon could have an Ability, a special trait that affected battles or exploration without requiring the player to select it as a normal move.

Abilities added strategic differences between Pokémon of the same species. For example, some could prevent status conditions, alter the effects of weather, or influence how attacks worked. The system made team-building more varied and became a permanent part of the main series.

Ruby and Sapphire also introduced Pokémon Contests, double battles, the Hoenn region, and 135 new Pokémon. Abilities are distinct from a Pokémon’s type: a Pokémon can be Fire-type, for example, while separately possessing an Ability such as Blaze or a different species-specific trait.