Which paired Pokémon games first introduced Pokémon Abilities to the main series?

Pokémon Ruby and Sapphire first introduced Pokémon Abilities to the main series.

Released for the Game Boy Advance in 2002 in Japan, the games began Generation III and added passive effects that could influence battles or exploration. For example, a Pokémon’s Ability might alter damage from certain moves, affect stat changes, or interact with weather.

Abilities gave individual Pokémon more mechanical identity beyond species, type, moves, and statistics. They also made team-building more strategic because two Pokémon of the same species could sometimes have different possible Abilities.

Ruby and Sapphire introduced the Hoenn region, double battles, Pokémon Contests, and many new species. Abilities remained a core feature in later generations, although their effects and availability have been revised repeatedly. They should not be confused with held items, another major battle feature that was introduced earlier in Generation II.