Waluigi is a recurring character in the Mario franchise, designed to be a rival to Luigi. His name is a combination of Luigi's name and the Japanese word warui (悪 い), which means "bad". He's also Wario's best friend.
He first appeared in Super Mario Tennis in 2000. Later, he is found in several spinn-off titles as a playable character.
Cunning but humorous, he is generally presented as a presumptuous person who gets angry easily. He rarely shows fair play; he quickly teases his opponent, starts dancing when he wins, and comforts himself, while he easily gets annoyed when his opponent is gradually progressing. Unlike Wario, he plans things before to act.
It is also revealed that Waluigi has a soft spot for Princess Daisy, who however pushes and hates him for his deceit, wickedness and ugliness. This element is undoubtedly one of the causes of his rivalry with Luigi.