Chaos is first introduced as a human fan of wrestling, named an 'otaku' by the other characters for his obsessive love of chojin and their culture, and is seen to be prone to panic attacks, as he endures flashbacks of a traumatic past. He is later revealed to be a Time Chojin, who is instrumental in Mantaro's success and saving the life of Kevin Mask.
When the Jikan Chojins used their "Legend" Destroying Bell, he suffered along with the other Chojin. He is the lone survivor of the massacre of his parents and fellow villagers. Remembering this incident causes him to go into violent fits, at which point he has to take a sedative (in the form of an asthma inhaler). During these fits, his fighting strength increases many fold, and he is able to compete at the same level as Neptuneman. After taking his medication, however, he forgets everything he did during his fit.
He works as a bogus Chojin Wrestler named Butanikuman (ブタ肉マン, Porkman), putting the money he earns into the Gakincho House orphanage he grew up in. Chaos has feelings for Rinko, although he also has a huge crush on singer Matsuda Seiko and has a collection of her merchandise.
Chaos is a very kind, although somewhat childish, character. He claims to be a human and not a Chojin. Chaos is a huge Chojin Otaku, and has a huge collection of Chojin-based goods (including Kinkeshi figurines). He will go through any means to add to his collection, even beat up his friend Kawazaki-kun.
He also has an odd obsession with pigs and giving people pig-themed gifts, most probably due to the fact that his earliest clear memory is living with a huge pig. He appears to greatly admire Idol Chojin Geronimo as a fellow "human fighting alongside Chojins".
A horn grew on the side of his head, as a child. Currently, the horn is gone and in its place is a keyhole shaped hole, which is a characteristic shared with the Time Chojin (he also has a design pattern on his body similar to them). He has long blond hair and pale skin, with a muscular physique.
Chaos grew up on Planet Avenir. 
He was trained by his father - the king - in Chojin Wrestling. One day, two mysterious figures attack his village and kill everyone except for him. After he escapes, he returns to his parent's graves and promises to avenge them someday and allow the Avenir Clan to live on. 
He somehow loses his memories, comes to Earth, and is found by Sister resting underneath a huge pig.  The pig looked at Sister and then walked into the woods, never to be seen again. Sister then took Chaos to Gakincho House and raised him as her own. Over the years he got stronger and also helped Sister raise the orphans, whom love him dearly and refer to him as An-chan (あんちゃん, Big brother). 
He uses his Chojin otaku knowledge to his advantage and gets a job with a bogus Chojin Wrestling show as Butanikuman.  Whatever money earned he doesn't spend on his Chojin goods collection he spends on gifts and food for the orphans. In 1983, he and his friend Kawazaki-kun attend the Universal Chojin Tag Tournament (the Dream Chojin Tag Arc). After Neptuneman flew into space to blow himself up, Chaos manages to obtain the Kinnikuman Great mask. Kawazaki-kun is actually the first to grab the mask, but Chaos smacks him around until he gives it up.
Chaos's future is so far unclear. 
During a time period known as the Justice Rest (正義の安息（ジャスティス・レスト）), many legends such as Kinnikuman, Terryman, and Robin Mask were raising their children, and others like Ramenman, Buffaloman, and Brocken Jr. were settling into retirement.  A wave of Brutal Chojin seized the opportunity and attacked Earth. In the Choujin Encyclopedia (超人大全, Choujin Taizen) this incident is referred to as the Rain of Brutality (残虐の雨, Zangyaku no Ame). They were defeated by a lone Justice Chojin.
The name of this chojin is unknown to Meat and Mantaro (due to Mantaro ripping the Encyclopedia page out and using it as toilet paper before Meat could read his name).  Mantaro is very sure that this man is Chaos, but Meat and Chaos himself are sceptical.  Furthermore, before the time-ship Kevin Mask can take off, Mantaro is sent out to remove a headstone that is blocking it's path.  The first letters in the name on the headstone are covered in dirt, but the last two letters are "ΘS". 
Chaos meets Mantaro and the others during one of his bogus Chojin Wrestling performances, during which he accidentally begins fighting for real after a pair of brass knuckles hit Rinko Nikaido. He is ganged up on by the other wrestlers until Mantaro saves him and they are chased out of the show by angry fans. He brings them back to the Gachinko House, where they see his huge Chojin Goods collection, which includes the Great Mask. Mantaro asks Chaos to pose as Kinnikuman Great and team up with him, but he refuses because he is actually a regular human. However, he changes his mind after Rinko dresses up like Seiko Matsuda and dances around for him.
As they enter for the preliminary Battle Royale, Chaos does many comical otaku-type things, such as filming a bootleg of the match, asking for autographs from all of the Chojin, and making a face print of Mongolman's face make-up. During the match, Mantaro tries his best not to tag Chaos in so as to protect him, but after Neptuneman and Seiuchin begin fighting Chaos is forced into the action. He is at first out-powered, but after he realises that he is bleeding, he becomes empowered through one of his episodes and begins fighting back. After he takes his medicine and calms down though, he is easily put in the Optical Fibre Cross Bomber, but is saved when Mantaro throws Seiuchin's head cover in the path of the technique.
After overhearing Meat tell Mantaro that teaming up with Chaos wasn't the best idea, Chaos runs away. However, after Sister helps him realize that the "key" to unlocking his memory is courage, he understands that he must go back and complete the tournament. Although Ikemen has to take his place during the lottery drawing, he makes it back in time for the first match. During their match against the Hell's Carpentors, his otaku knowledge helps them defeat PlaMoman's plastic model techniques, but his inexperience against Chojins causes many problems and he soon goes into another one of his fits. They try to win with the Muscle Docking, but Chaos becomes too scared to complete it, forcing Mantaro to defeat Deiku Toryu with a Muscle G. With support from Mantaro, Rinko, Sister, and the others, he is finally able to defeat PlaMoman with a Power Bomb, earning a victory for the Muscle Brothers Nouveau. Afterwards, the four competitors become friends.
Chaos is later seen watching the Reserve Match between the Five Disasters and the Handblades. He reveals that he greatly admires Geronimo, both being humans who fought alongside the Seigi Chojins. Chaos later trains alone in the rain, until Rinko arrives with his old friends from the Bogus Chojin Wrestling Show. Recently, Chaos was greatly surprised to learn that Mari Nikaido was Rinko's mother.
The Muscle Brothers Nouveau are currently fighting the 20 Million Powers in an Electric Cage Match. Because they are a newly formed team, they have yet to master the timing of their combo attacks and are soon overpowered by the 20 Million Powers. Recently, Chaos' memories have been restored and his aura tore apart the Great Mask and costume. He unleashed a series of attacks on Buffaloman proving he is more the he appears to be. During the fight the 20 Million Powers used the Long horn train but, they countered also using the Long Horn Train using Chaos's legs as the horns. It caught the 20 Million Powers off guard then Chaos puts the Japanese leg roll on Mongolman, while Mantaro puts Buffaloman in the Muscle G making their new move the Muscle Evolution. The move defeats the duo and destroys the Mongol Mask.
Chaos later dies during this same arc. He is replaced by Kevin Mask in "Muscle Nouveau", who has made a full recovery, and Kevin fights initially in Chaos' "Great" mask, before he wins the final match in Chaos' honour. Chaos is buried in the grave seen at the start of the arc, in which only the stylised 'OS' remained. He can be seen in spirit several times, offering inspiration to those around him.
W Kinniku Buster
Chaos Sphere Bottom
King German Suplex
Muscle Docking (failed)
- Saviour of the Interval (間隙の救世主, Kangeki no Kyuuseishu)
- The Man who Creates Legends (伝説を作り出す男, Densetsu wo Tsukuridasu Otoko)
- Saviour of the Era (時代の救世主, Jidai no Kyuuseishu)
- Win/Loss Record (Singles)
- O Minutes Avenir (King German Suplex)
- O Itto Mask, Robin Mouse (W Kinniku Buster)
- Win/Loss Record (Tag)
- Kinnikuman Manias (Mantaro Kinniku)
- O Beefman, Curry Lou Thesz, Faux Lupin (Arm Hook Double Dropkick)
- O Tenmusuman (Double Brainbuster)
- O Itto Mask (Unnamed Combo Technique)
- Muscle Brothers Nouveau (Mantaro Kinniku)
- Δ Hell Expansions (Interference) (as Great III)
- O Hell Carpenters (Muscle Gravity) (as Great III)
- O 20 Million Powers (Muscle Evolution) (as Great III)
- O The Machineguns (Muscle Evolution)
- Submitted by: Megumi Kaneda (兼田恵) of Kanagawa and Ōshaku Yoshida (吉田大錫) of Osaka
- Least Favourite Food: Beni shoga
- Favourite Celebrity: Seiko Matsuda
- He refers to himself in the first person as Wachiki (ワチキ), occasionally using the more common Boku (ボク). He also refers to Sister as Mother (マザー).