Which game was the Pokémon series’ first true 3D role-playing installment?

Pokémon Colosseum was the Pokémon series’ first true 3D role-playing installment.

Developed by Genius Sonority for the Nintendo GameCube, Pokémon Colosseum combined a story-driven role-playing structure with fully modeled 3D environments and battles. It was released in Japan on November 21, 2003, before reaching North America and Europe in 2004.

The game takes place in the desert region of Orre and follows Wes, a former member of Team Snagem. Instead of finding most Pokémon through ordinary wild encounters, players rescue Shadow Pokémon and use a Snag Machine to capture them from opposing Trainers.

Pokémon Stadium and Pokémon Stadium 2 had already shown Pokémon battles in 3D on Nintendo 64, but they were primarily battle-focused console companions rather than full role-playing adventures. Pokémon XD: Gale of Darkness followed Colosseum as a related GameCube role-playing game.