Which Pokémon games first introduced Abilities as a standard gameplay feature?

Pokémon Ruby and Sapphire first introduced Abilities as a standard gameplay feature.

Released for the Game Boy Advance in Japan in 2002, Ruby and Sapphire began Pokémon's third generation. Each Pokémon could possess an Ability that affected battles or exploration, adding another layer beyond types, moves, and statistics.

Examples include weather-related effects, immunity to certain moves, and changes to battle conditions. Abilities became a permanent part of the main series and have remained important in team building.

Earlier games introduced other major systems, including breeding in Gold and Silver and the original type-based battle framework in Red and Green. Those features are sometimes incorrectly credited with Abilities, but the mechanic began with Ruby and Sapphire.