Wario

(Japanese: ワリオ) is an obese yet surprisingly muscular, short, hot-tempered, greedy character and Mario's yellow-and-purple clad rival. Wario's greed pushes him to commit evil acts, such as the seizing of Mario's Castle. Due to his money grubbing personality, he is not liked by many citizens of the Mushroom Kingdom. Wario has also proven to be very cunning as he has tricked Mario on more then a few occasions. He often goes out on his own adventures; from stealing treasure to running a mini-game making company. Wario has helped heroes of the Mushroom Kingdom on a few separate occasions as well.
According to the Wario World instruction manual, Wario weighs 308 pounds, although he claims it's just his clothes ("I like to layer!"). He has a black mustache and impressive, muscular arms despite his weight problem. He commonly wears tight purple overalls over a yellow shirt with green elf-like shoes and a yellow hat.Wario is prone to outbursts of anger, especially when he doesn't get his way. He has unhygienic habits, such as nose picking, and it's clear what he cares most about is himself, and money.
His shoes and pointed ears make him looks uncannily like an elf. Also, his colors (yellow and purple) are complementary colors in the color wheel, suggesting Wario's imbalance.
Strangely, unlike Waluigi, Luigi, and Mario, Wario's outfit is slightly different. Wario has cut off his long sleeves he had in Mario Party's 1 - 4 and various sports games up until then. Now, he sports the short sleeve shirt he has had in the Wario Land series games.
It's also noted that Wario's colors don't compute with the other plumbers who wear similar outfits- Mario, Luigi, and Waluigi. He has a white streak on the rim of his yellow hat, and has white buttons instead of the usual yellow. Additionally, the W on his cap sticks out of the white spot it is displayed on.
Wario's clothing also breaks the palette-swap color scheme in place from Mario and Luigi. Mario and Luigi have the same colored pants, with their signature colors being opposites (red and green). With Wario and Waluigi, while the signature colors are still oppsites (yellow and purple), their pants are not matching colors.
It is also shown that Wario may be bald. In an animated commercial for Super Mario Land 2: 6 Golden Coins, Wario is shown with no cap on. He is completely bald in the commercial, although it may not be relevant to the video games. Tiny Wario has been consistently drawn with a small mohawk, and standard Wario is shown to have hair in Mario Kart 64 (in his profile picture after a loss, which shows him biting his cap) and Super Mario 64 DS (if his cap is stolen or knocked off).
Wario's outfit is referenced in the game Paper Mario: The Thousand-Year Door when the player wears the W Emblem badge, thus dressing Mario in Wario's yellow shirt and purple overalls.
His strength is many times stronger than a normal man. He is fat but has extraordinary arm strength. He is so strong that his strength exceeds his rival Mario and rivals that of Donkey Kong and even the powerful Bowser. In Wario World, Wario could use his strength to punish his enemies in a variety of ways, including the Piledriver, Corkscrew Conk, and Wild Swing-Ding.
Wario is commonly associated with explosives, including Bob-ombs, and ways of stealing coins, such as a magnet or even a large vacuum of sorts.
Wario's greatest strength, though, is with items, such as the Garlic Pot, Jet Pot, Bull Pot, and Dragon Pot, which give him amazing and unique transformations. He also shares some transformations with Mario such as Fire Wario and Metal Wario. Wario has other various ways in transformings, resulting in transformations such as Crazy Wario, Flat Wario, Fat Wario, Frozen Wario, Electric Wario, and many more. Wario also has the power of farting to stun his opponets.Wario is a greedy person, to a pig-like extent. He is so greedy, he will do anything to get money, be it stealing or going on an adventure. He is also a miser, as he never lets anyone touch his treasure. He can also be seen stuffing his face often like a pig, indicating that his greed is extended to food. Alas, his greedy nature overtakes him and he goes out of control occasionally, even going as far as to double-cross his friends. Like Mario, he has many Italian traits. While he is of Italian heritage, whether he was actually born in the country Italy or not is still a mystery due to the lack of information on his birthplace. Nintendo Power once stated that Wario is Mario's cousin.
Wario's not as dumb as he appears to be since he makes WarioWare games and can fly a plane. In fact, he may actually be very skilled at electronics, as he made a dimensional teleporter in a few seconds. He also constructed the Mario Kart 64 race track Wario Stadium. The reason why many assume he is a bonehead is that he is hot-headed, clumsy, and sometimes forgets his common sense.
Wario is very aggressive, especially in the Mario Kart series, as he pushes racers off the road if in his way. In the Mario Party series, he apparently puts his greedy nature aside to play fair, if that's even in his vocabulary. In general sports, Wario is a braggart and a sore loser, even going as far as to claim that somebody is cheating when he loses.
According to the official website for Wario Land 4, Wario excersises during his free time, and according to the Choose Your Own Adventure book Warioland 4, Wario hates sand. 
Wario is considered scary to most of the Toads (though not as scary as Bowser), as revealed in Super Mario 64 DS.