Which Pokémon game introduced the Pokémon Contest competition system?

Pokémon Ruby and Sapphire introduced the Pokémon Contest competition system.

Released for the Game Boy Advance in 2002 and 2003, these games added a parallel activity in which Pokémon competed in categories such as Coolness, Beauty, Cuteness, Cleverness, and Toughness. Contest performance depended on attributes, move effects, and appeal rather than simply defeating an opponent in battle.

Ruby and Sapphire also introduced the Hoenn region, double battles, abilities, natures, and 135 new Pokémon. The original Contest system was later expanded and redesigned in games including Diamond and Pearl. Pokémon Contests are sometimes confused with Pokémon Super Contests, but Super Contests are the later Sinnoh version of the idea.