Which Pokémon game pair introduced Abilities to the series?

Pokémon Ruby and Sapphire introduced Abilities to the Pokémon game series.

Released for the Game Boy Advance in Japan in 2002, Ruby and Sapphire added Abilities as permanent traits that can affect battles or exploration. Examples include Levitate, which grants immunity to Ground-type moves, and Intimidate, which lowers an opposing Pokémon’s Attack when the Pokémon enters battle.

Abilities are separate from moves, types, and held items. A Pokémon’s Ability can work automatically, often when it enters battle or when a specific condition occurs. This added a new layer of strategy beyond choosing attacks and managing type matchups.

Gold and Silver introduced held items, breeding, and Pokémon genders, but not Abilities. Diamond and Pearl and X and Y expanded the Ability system later, which can make their prominent competitive mechanics seem older than they are.