Which Pokémon video-game generation first introduced Abilities?

Generation III first introduced Abilities to the Pokémon video-game series.

Abilities are passive powers assigned to individual Pokémon that can affect battles, exploration, or other game mechanics. They debuted in Pokémon Ruby and Sapphire, the Generation III games for Game Boy Advance, released in Japan in 2002.

Examples include Torchic's Blaze, which strengthens Fire-type moves when its health is low, and Slaking's Truant, which limits how often it can act. Abilities added another layer of strategy beyond a Pokémon's type, moves, statistics, and held item.

Generation II did introduce held items, breeding, and Pokémon natures' predecessors through several new systems, but not Abilities. Some later Pokémon can have more than one possible Ability, and hidden Abilities were added much later. The original Ability system therefore belongs specifically to Generation III.