Mario is the character most commonly associated with the Mario Party series. As Nintendo’s flagship mascot and the namesake of the franchise, he appears prominently across the games, promotional material, box art, and storylines.
The series is built around Mario and his friends competing in board-game-style contests. The original Mario Party includes Mario, Luigi, Peach, Yoshi, Wario, and Donkey Kong as playable characters, with each of the first six boards themed around one of those characters. Mario is also the central figure in the broader franchise from which the series takes its characters and settings.
Bowser, Peach, and Luigi are all strongly associated with Mario Party too, but none is the series’ primary namesake or mascot. Bowser usually acts as an antagonist or disruptive event character, while Peach and Luigi are frequent playable competitors. Their importance explains why they may appear in the answer choices, but Mario remains the canonical association.