Waluigi (English: /ˌwɑːluˈiːdʒi, ˌwɒl-/ ^ⓘ) is a character in the Mario franchise. He plays the role of Luigi's arch-rival and accompanies Wario in spin-offs from the main Mario series, often for the sake of causing mischief. He was created by Camelot employee Fumihide Aoki and was voiced from 2000 to 2022 by Charles Martinet, who described Waluigi as someone with a lot of self-pity. Waluigi's design is characterised by his tall stature, thin and lanky frame, and his purple and black outfit with a purple hat, which displays an inverted yellow "L".

He was designed as Wario's tennis partner and sidekick, debuting in the 2000 Nintendo 64 game Mario Tennis. He has featured in over 50 video games, appearing in at least one game every year since his debut until 2022. He is a playable character in Mario sports games, most Mario Party games, and also in the Mario Kart series. He has also made cameo appearances in other video games, such as the Super Smash Bros. series.

Since his debut, Waluigi has received a polarised reception from the media, often being accused of having few defining characteristics and minimal backstory. He has attained a cult following, especially helped through his use as an Internet meme. Although he has never appeared in his own video game or any mainline Mario game, critics have described him as one of Nintendo's mascots and a cult hero.

Waluigi was created during the development of the game Mario Tennis to serve as the bitter rival to Luigi. He was originally introduced as Wario's younger brother in the American version of the game. His character design was created by Fumihide Aoki. His name is a portmanteau of Luigi's name and the Japanese adjective warui (悪い), meaning "bad"; hence, a "bad Luigi".

Waluigi was conceived as a sidekick for Wario to team up with in the doubles matches of Mario Tennis. In an interview with Nintendo Dream, Shugo Takahashi said that he initially asked Nintendo to create a new character but was told to develop a character at Camelot. The character's name was agreed upon from the beginning before his design was finalised. Initially, the idea was to change one letter to make him similar to Wario, but Takahashi said that as a bad version of Luigi, he was named Waluigi. An early idea for the symbol on Waluigi's hat was a W, but as this was the same as Wario, it was changed to the letters W and L. Yōichi Kotabe, who supervised the character at Nintendo, decided that this should be an upside-down L as an inversion of Luigi, just as the W in Wario is an upside-down M for Mario. Waluigi's appearance was designed to be lean to create a balanced team combination with the stoutness of Wario. Camelot took inspiration from Boyacky and Tonzura from the Doronbo Gang in the Yatterman series. His purple colouring was chosen to create a balance of colours alongside those of the other characters in the game, and his moustache was created in the shape of the letter L. Takahashi said that Waluigi was characterised as the rival of Luigi, with them having a similar relationship to Mario and Wario.

Upon his debut in Mario Tennis, Waluigi was voiced by Charles Martinet, who continued to voice the character until stepping back from recording character voices in 2023 to take on a new role as Mario Ambassador at Nintendo.

Waluigi's appearance in Super Mario Strikers gained attention for a celebratory taunt that became known as the "crotch chop". The taunt involves the character thrusting his hips forward while gesturing towards his crotch. Despite looking like the letter V, Waluigi's chop using both hands was supposed to represent the W in his name. The game's director, Mike Inglehart, said that the development team at Next Level Games wanted to make Waluigi "a bit edgier than Wario" and explore his character. He thought that Waluigi's character was about blaming others, whereas Wario was about self-loathing. Inglehart said that when it was presented to Nintendo, "nobody batted an eye", so he was surprised that the taunt was allowed to remain in the game without question.

Waluigi is portrayed as a mischievous villain and an exaggerated mirror version of Luigi. He bears a large pink nose and crooked moustache. His stature is tall, and his frame is thin and lanky. He is the rival of Luigi and is the same age. His Super Smash Bros. Melee trophy describes him as hardworking by stating that he spends his time training and perfecting his skills in order to antagonise the Mario brothers. Although he has a scrawny physique, Waluigi is technically skilled and athletic but sometimes cheats in-game. His design comprises black overalls, a purple long-sleeved shirt, and a purple hat with a yellow "Γ" symbol (an inverted L, paralleling Wario's W as an upside-down M).