Which generation introduced Pokémon Abilities in the core game series?

Generation III introduced Pokémon Abilities in the core game series.

Abilities debuted in Pokémon Ruby and Sapphire, which launched in Japan in 2002 for the Game Boy Advance. An Ability is a passive trait that can affect battles or exploration, sometimes activating automatically when a Pokémon enters battle or when a particular condition occurs.

Examples include Intimidate, which lowers an opposing Pokémon’s Attack when the user enters battle, and Levitate, which grants immunity to Ground-type moves in the relevant game mechanics. Abilities added another layer of strategy beyond moves, types, and statistics.

Generation III also introduced Natures and double battles. The mechanic should not be confused with held items, which were introduced in Generation II and are separate from a Pokémon’s inherent Ability.