Wa-ha-ha! Waluigi, number one!
~ Waluigi

Waluigi is Luigi's arch-rival and Wario's partner/younger brother. He first appeared in Mario Tennis for the Nintendo 64 in 2000.

Despite being a villain in Mario Sports titles and in Dance Dance Revolution: Mario Mix, Waluigi is one of the main playable characters in the Mario Party series and is an ally to Mario in the Mario Party series, except for Mario Party 3's story mode where he acted as a villain. He appeared in the Mario Kart series as a playable character since Mario Kart: Double Dash!!, he also appeared in Mario Kart DS as an unlockable character, and Mario Kart Wii as a playable character again, but in Mario Kart 7, Waluigi did not return as a playable character, but made a cameo in DS Waluigi Pinball.

Waluigi eventually appeared in Mario Kart 8 as a playable character once again. Waluigi was an unlockable character four times, in the Game Boy Color version of Mario Tennis, Mario Golf: Advance Tour, Yakuman DS, and Mario Kart DS. The Game Boy Advance version of Mario Power Tennis was the first and only Mario game that Waluigi is seen without Wario. He also appears as an assist trophy in Super Smash Bros. Brawl in Super Smash Bros. 4. He only appears in Mario spin-off titles.