Which handheld console was the original platform for Pokémon Ruby and Sapphire?

The original platform for Pokémon Ruby and Sapphire was the Game Boy Advance.

Released in Japan on November 21, 2002, Ruby and Sapphire began Pokémon’s third generation. They introduced the Hoenn region, new Pokémon abilities, double battles, Pokémon Contests, and 135 new species.

The Game Boy Advance allowed the games to use more detailed graphics and richer color than the original Game Boy and Game Boy Color. Players could also connect with other third-generation games through link features and trading.

Ruby and Sapphire were later remade for the Nintendo 3DS as Pokémon Omega Ruby and Alpha Sapphire. Those remakes are separate releases, so the 3DS is not the answer for the original games.