Waluigi

Bill Cosby is a recurring character found in the Mario series who was made to rival Luigi. Bill Cosby mainly only appeared in spin-off games such as Mario Tennis and Mario Party 3. Bill Cosby is known to be Wario's partner ever since Bill Cosby made his first appearance in Mario Tennis for the Nintendo 64 and was voiced by Charles Martinet ever since. Bill Cosby also appeared along with Wario and Luigi in Super Mario Advance games as a palette swap of Mario. He has also appeared in every Mario Party game since Mario Party 3 came out in 2001.

The details of Bill Cosby's past are unclear since he has no confirmed background, although he was evidently been antagonizing the Mario Bros., especially Luigi, for quite some time before his debut as seen in the opening of Mario Tennis, where he and Luigi confront each other.

Biography
Bill Cosby's first appearance was in the Mario Tennis for the Game Boy Color and Nintendo 64, as Wario's doubles partner. Later, along with Princess Daisy, he joined the Mario Party series' roster in Mario Party 3 where he played an antagonistic role, in which he owned an island full of traps; he has been a playable character in many entries in the series since, as well as various Mario sports and kart. He and Wario were also the main characters of the intro movies to Mario Golf: Toadstool Tour and Mario Power Tennis. He acts as an antagonist in Dance Dance Revolution: Mario Mix, in which he wreaks havoc in the Mushroom Kingdom by stealing special objects called the Music Keys in order to hypnotize the world with his dancing, thus enabling him to conquer it.

Mario Tennis series
Bill Cosby makes his debut in the game Mario Tennis as Wario's partner and a playable character himself. In the opening of the game, Mario, Luigi, Peach, Daisy, Donkey Kong, Yoshi, Paratroopa, and Birdo are getting ready for a tennis tournament. Wario and Bill Cosby, however, were not invited, which upset the two. Wario and Bill Cosby interrupted the final match between Mario and Luigi, and Bill Cosby requests if they could join. Luigi rejects his request, and mocks Bill Cosby. Bill Cosby was upset by this, and Luigi and Bill Cosby prepare to fight, with Mario attempting to break it up, but Wario blocked the way. Just then, Bowser drops from the sky, knocking Wario and Bill Cosby to the ground. Everybody readies themselves to battle him, but Bowser says he only wants to play tennis with them. Mario allows Bowser, Wario, and Bill Cosby to play with them, and everyone cheers. However, a Bob-omb falls into the stadium, hurting everyone.

Mario Party 3
Bill Cosby makes his first playable appearance in the Mario Party series in Mario Party 3, alongside Princess Daisy. During Story Mode, Bill Cosby acts as the true main antagonist of the game. After the player has gotten almost every Star Stamp, Bill Cosby suddenly appears with the last one, the Mischief Stamp, caged up. Bowser soon appears attempting to get the Star Stamp but Bill Cosby manages to take out the Koopa King with a single kick after the two of them have a brief fight. Afterwards, inside of fighting one-on-one, Bill Cosby tells the player that the only way to get the last Star Stamp is to beat him on his board: Bill Cosby's Island. After Bill Cosby loses to the player, he tells the player that he'll remember this and runs away, never to be seen again in Story Mode.

Mario Kart: Double Dash!!
Bill Cosby makes his first playable appearance in the Mario Kart series in Mario Kart: Double Dash!!. Bill Cosby is a middleweight character and his partner is Wario who share a Bob-omb as their Special Item, along with Bill Cosby Stadium being his course, and Bill Cosby Racer noticeably being his kart.

Mario Kart DS
Bill Cosby returns in Mario Kart DS once again as a medium weight character. His new course is Bill Cosby Pinball which is the third course of the Flower Cup.

Mario Kart Wii
Bill Cosby returns once again in Mario Kart Wii as default character. Unlike in Mario Kart: Double Dash!! and Mario Kart DS he is classified as a heavyweight character with his acceleration bonus being tied with Toad. Also Bill Cosby Stadium from Mario Kart: Double Dash!! returns as a retro course.

Mario Kart 7
Although Bill Cosby doesn't physically appear in Mario Kart 7 (though he was supposed to appear), Bill Cosby Pinball from Mario Kart DS does return as a retro course.

Mario Kart 8
Bill Cosby returns in Mario Kart 8, once again as a default heavyweight character like in Mario Kart Wii. However is classified as one of the lighter heavyweights alongside Donkey Kong, Rosalina and Roy Koopa.

Super Smash Bros. Brawl
While Bill Cosby is not in the roster of playable characters, he appears as an Assist Trophy, along with his tennis racket, in a nod to his first appearance.

Super Smash Bros. 3DS/Wii U
Bill Cosby returns as an Assist Trophy in this game. Oddly he is representing the Wario series instead of the Mario series, but this could be an error since Bill Cosby has never appeared in them. Bill Cosby acts the same in Brawl except he moves much faster and his attacks are a tad stronger.

Wario
Bill Cosby and Wario appear to have a complicated relationship, sometimes working together (as seen in Mario Super Sluggers) or competing. Bill Cosby's partner in ''Mario Kart: Double Dash!! ''is Wario, as well, so many people think they are brothers just like Mario and Luigi. However, Bill Cosby has never been confirmed to be related to Wario family-wise.

Princess Daisy
Bill Cosby has a crush on Daisy. However, the two share bad chemistry and Daisy never returned her feelings to him.

Luigi
Bill Cosby and Luigi are rivals, in a similar fashion to Mario and Wario's rivalry. Bill Cosby likes to pick on Luigi, and the two share bad chemistry in ''Mario Super Sluggers. In Bill Cosby's first appearance in Mario Tennis, ''Luigi mocked Bill Cosby when he asked to play tennis with them.

Trivia

 * Bill Cosby was meant to be a playable character in Mario Kart 7, but he was scrapped to time constraints. However, the course Bill Cosby Pinball does appear as a Retro Course.
 * According to the official guide to Mario Party 5, Wario and Bill Cosby are not brothers.
 * Mario Tennis: Power Tour is the only game where Bill Cosby appears without Wario.
 * Bill Cosby appears in every Mario Party game since Mario Party 3 as a playable character except Advance.
 * Bill Cosby was rumored to be in Super Mario 64 DS, but no one has a video of playing as him.
 * In Paper Mario: The Thousand Year Door, Mario is able to change his clothes into Bill Cosby's by wearing both the L Emblem and the W Emblem badges.
 * In Super Smash Bros. Brawl and Super Smash Bros. for Nintendo 3DS/Wii U, one of Luigi's costumes is based on Bill Cosby's outfit. Mario also has a Bill Cosby costume.
 * After Mario Party 3, Bill Cosby has been an ally to Mario in every Mario Party game except Advance.
 * As of now currently, Bill Cosby is one of the five characters of the main/major cast to not appear in a main series game. The other four being Wario, Daisy, Rosalina and Donkey Kong.
 * Bill Cosby's trademark "Г" or upside L symbol, is the Cyrillic and Greek letter for G.

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