Wario (English: /ˈwɑːrioʊ, ˈwær-, ˈwɒr-/ ^ⓘ) is a character in Nintendo's Mario franchise that was designed as an antithesis of Mario. Wario first appeared as the main antagonist and final boss in the 1992 Game Boy game Super Mario Land 2: 6 Golden Coins. His name is a portmanteau of the name Mario and the Japanese word warui (悪い), meaning "bad". He is usually portrayed as a selfish and greedy treasure hunter who, in karmic irony, routinely loses his spoils by adventure’s end. Since his debut, he has appeared in the majority of Mario video games. Hiroji Kiyotake designed Wario, and Charles Martinet voiced the character from 1993 to 2023.

Wario is also the main protagonist and antihero of the Wario Land platformer series and the WarioWare party game series. He makes regular appearances as a playable character in Mario spin-offs and other video game series, including Mario Sports games, Mario Kart, Mario Party, in which he is typically paired with the character Waluigi to form a comedy duo that rivals the partnership of Mario and his brother, Luigi. Wario has also been featured in several entries of the fighting game series Super Smash Bros..

The character Foreman Spike, a possible inspiration for Wario, first appeared in the 1985 game Wrecking Crew. Spike is a construction foreman who bears a slight resemblance to Wario. Game artist Hiroji Kiyotake designed Foreman Spike, whom Kiyotake imagined as "the Bluto to Mario's Popeye". Wario's first named appearance occurred in the 1992 game Super Mario Land 2: 6 Golden Coins. Wario's design arose from Super Mario Land's design team's distaste for making a game based around someone else's character. The creation of Wario allowed them their own character to "symbolize their situation".

Wario is portrayed as a caricature of Mario: he has a large head and chin; huge muscular arms; a wide, short, slightly obese body; short legs; a large, pointier, zig-zagging mustache; and a bellicose cackle. He wears a plumber outfit with a yellow-and-purple color scheme, which is a short-sleeved yellow shirt, purple overalls, and a blue "W" on his hat. He also wears green shoes and white gloves with blue "W" symbols. In his early appearances, Wario wears a yellow, long-sleeved shirt and fuchsia overalls. The name "Wario" is a portmanteau of "Mario" and the Japanese adjective warui (悪い), meaning "bad", hence "bad Mario", which is also symbolized by the "W" on his hat (an upside-down "M"). Wario was planned to be a temporary name, but it proved popular with the staff. Waluigi was created to be the tennis partner of Wario in Mario Tennis and early material from Nintendo of Europe portrayed them as brothers, but their relationship has since been ambiguous. When asked whether Wario was a brother to Waluigi in 2008, voice actor Charles Martinet stated that while he did not know, he felt that they were just "two nice, evil guys who found each other".

Nintendo originally considered making Wario a German character before he developed into an Italian like Mario. Wario was intended to be German at one point; German translator Thomas Spindler gave him German lines when he was brought on to voice Wario. This part of Wario was eventually dropped; Martinet's Wario voice did not have any German influence. During his audition for the part, Martinet was told to speak in a mean-and gruff-sounding tone; he said voicing Wario is a looser task than voicing Mario, whose speaking manner and personality are freer-flowing, rising from the ground and floating into the air, while jealousy is one of Wario's characteristics.

Wario is often portrayed as a villain in video games in which he makes a cameo appearance. The development team for Wario Land: Shake It! stated he was not really a villain, and they did not consider him one during development. They focused on his behavior, which alternates between good and evil. Etsunobu Ebisu and Takahiro Harada, producers of Shake It!, considered Wario to be a reckless character who uses his strength to overwhelm others. Tadanori Tsukawaki, Shake It!'s design director, described Wario as manly and said he was "so uncool that he ends up being extremely cool." Because of this, Tsukawaki wanted Wario to act macho rather than silly and asked the art designers to emphasize his masculinity. During an interview with Kikizo, video game designer Yoshio Sakamoto, who was a member of R&D1 since its early days, stated the project centered around Wario because the team "couldn't think of anyone else best for the role", and he was then described as "unintelligent" and "always idiotic", which is the reason he was chosen as the star of the WarioWare series. According to an early 1990s Nintendo guide, Wario was Mario's childhood friend, which Kotaku later contested in a parody article. Afterward, it was stated that they were not related to each other and were considered childhood rivals.

In his earliest appearances in Super Mario Land 2: 6 Golden Coins and Wario's Woods, Wario displays considerable magical power, using spells on the population of islands to turn them into his minions, create duplicates, and grow very large. These traits were discontinued starting with Wario Land: Super Mario Land 3, in which he is rejuvenated by garlic in a similar manner to Mario being powered by mushrooms. In the WarioWare series, he became as a smelly slob, while in Mario Strikers: Battle League, his super shot special involves smashing his butt into the ball, followed by him devouring a giant clove of garlic. In WarioWare: Touched!, consuming garlic transforms Wario into "Wario-Man", a superhero with powers relating to garlic-induced flatulence and bad breath. In other games, he uses farts as his special attack. Wario prominently uses bombs as tools and weapons in the WarioWare series as a visual motif to represent the time limit of a microgame.

Wario first appeared as a villain in the 1992 Game Boy video game Super Mario Land 2: 6 Golden Coins, in which he captures Mario's castle. Tatanga, the villain of the first Super Mario Land game, is a henchman of Wario in the second, implying Wario is responsible for the events of both games. Wario also serves as a villain in the 1993 Japan-only puzzle game Mario & Wario, in which Wario drops a bucket on the heads of Mario, Princess Peach, or Yoshi. This was followed by the first game in the Wario Land series, Wario Land: Super Mario Land 3 (1994), a platform game that marks Wario's first appearance as a protagonist and introduced his first villains, Captain Syrup and her Brown Sugar Pirates. In his next appearance in Virtual Boy Wario Land (1995), Wario plays similarly and has the ability to move in and out of the background. A sequel to the Game Boy game Wario Land II (1998) features Captain Syrup's return as the antagonist. This game introduces Wario's invulnerability, allowing him to be burned or flattened without sustaining damage.