Kinnikuman (キン肉マン; lit. transl. "Muscle Man") is a Japanese manga series created by the duo Yoshinori Nakai and Takashi Shimada, known as Yudetamago. It follows Suguru Kinniku, a superhero who must win a wrestling tournament to retain the title of prince of Planet Kinniku. Nakai and Takashi planned the series when they were attending high school originally as a parody to Ultraman.

The manga was originally published in Shueisha's shōnen manga magazine Weekly Shōnen Jump from 1979 to 1987, and was first adapted by Toei Animation into a 137-episode anime series broadcast on Nippon Television from 1983 to 1986. It restarted publication in 2011 in Shueisha's web magazine Shū Play News, and has spawned spin-off manga and anime series, video games, anime films, and several Kinnikuman-related merchandise.

There is also a sequel, the Kinnikuman: The 2nd Generation (キン肉マンII世, Kinnikuman II Sei; known as Ultimate Muscle outside Japan) manga that was serialized in Weekly Playboy between 1998 and 2004. It was published in North America by Viz Media under the title of Ultimate Muscle. It was also adapted into three different television series, all of which were broadcast on TV Tokyo in Japan and released in North America by 4Kids Entertainment.

Kinnikuman is one of the best-selling manga series in Japan, with over 85 million copies in circulation by 2025. As popular as was the anime series and its merchandise, such as Kinkeshi, a line of action figures released as M.U.S.C.L.E. in North America. It received the Shogakukan Manga Award for children's manga in 1984.

A new anime television series adaptation produced by Production I.G, based on the 2011 revival manga and celebrating the 40th anniversary of the original anime television series, aired from July to September 2024 on CBC and TBS' programming block Agaru Anime [ja], and was released worldwide on Netflix. The second season aired on the same programming block between January and March 2025. A third season has been announced.

The story involves Kinnikuman (real name Suguru Kinniku), a clumsy, foolish, comical superhero who discovers that he is the missing prince of the planet Kinniku (known for producing the greatest superheroes in the universe). Since he is a clumsy fool, however, he must prove himself worthy of the throne. To do so he enters wrestling competitions and battles evil Chojin, culminating in a tournament between Kinnikuman and five pretenders to the throne: Kinnikuman Big Body, Soldier, Zebra, Mariposa and Super Phoenix. Many of Kinnikuman's allies begin as villains (Ramenman, Buffalo Man, Ashuraman and Warsman) or arrogant heroes (Terryman, Robin Mask and Wolfman). The heroes and villains are collectively known as Chojin, which literally means "supermen".

Mantaro Muscle (also known as Kid Muscle, Mantaro Kinniku in the Japanese version) is the spoiled son of superhero wrestler King Muscle (Kinnikuman in the Japanese version). After 28 years of peace, the Seigi Choujins' (Muscle League) old enemies regroup and form the Demon Manufacturing Plant (dMp, known in the English version as Destruction, Mayhem and Pain). The Muscle League has lost its edge and are overwhelmed by the young, well-trained fighters. Recognizing their weakness, the Seigi Chojin reopen the Hercules Factory (a school for superheroes) and begin training a new generation of heroes to take on the dMp. At first unwilling, Mantaro (Kid Muscle) is one of the young heroes and defeats his father to prove his readiness to graduate. He and the other new Seigi Choujin defeat several members of the dMp and meet Kevin Mask, who quits dMp when he discovers their lack of honor. They also battle Sunshine and his pupils, who destroy the dMp after developing a renewed respect for the fighting spirit of the Seigi Choujins. The manga continues with the New Generation Replacement Tournament, Mantaro's challenge to master his inherited potential (Kajiba no Kuso Chikara, "burning inner strength" or "the fire"), the return of the Chojin Olympics, a fight with the Demon Seed (a villainous group), a backstory for Robin Mask and a tag-team tournament set in the past. Although the manga begins as a fairly lighthearted, humorous (albeit violent) story, later arcs (the No Respect and Demon Seed storylines in particular) have a darker tone and frequently deal with psychological trauma.

Yoshinori Nakai and Takashi Shimada (collectively known as "Yudetamago"), friends since fourth grade, decided to create a manga series in high school. Before its regular publication, the series (originally a parody of Ultraman) was released as two one-shots in Shueisha's magazine Weekly Shōnen Jump in December 1978 and March 1979: Okamarasu no Maki, which won the Akatsuka Award, and Eraginesu no Maki. Kinnikuman was serialized in the same magazine from the May 28, 1979, to the May 4, 1987 issues. Shueisha collected its 387 chapters into 36 tankōbon, releasing them from February 15, 1980, to April 15, 1988.