Chaos (Sonic)

"You know nothing, fool! It's Chaos, the god of destruction!"

- Dr. Eggman about Chaos. "Chaos, the ultimate water user."

- Dr. Eggman about Chaos

Chaos is a powerful water-based creature in the Sonic the Hedgehog series. He is a mutated Chao and guardian of the Chaos Emeralds that takes the role of the main antagonist of Sonic Adventure, appears as a minor villain in his Perfect form as a boss in Sonic Generations and will appear as one of the main antagonists in Sonic Forces.

History
Chaos was once a regular Chao, but became mutated by the power of the Chaos Emeralds. He became their guardian, as well as the guardian of the Chaos Emeralds. One day, an ancient tribe of Echidna discovered the shrine, and wished to use the power of the emeralds to conquer the world. Tikal stood in their way, telling them what they were doing was wrong. They payed her no attention, and attacked the shrine. In the process, they stomped on all of Chao who lived there. This enraged Chaos, who used the powers of the Chaos Emeralds to destroy the entire Echidna civilization. Tikal used the power of the Master Emerald to seal Chaos and herself away, before he could bring destruction to the rest of the world.

Sonic Adventure
Knuckles, the last surviving member of the Echidnas, was placed in charge of guarding the Master Emerald on Angel Island. He didn't know why, but regardless he knew it was his duty. One day, while dozing off, he awoke to the sight of a shattered Emerald, and a strange being, Chaos standing in front of him. Chaos got away, and Knuckles started his quest to repair the Master Emerald. Eggman was able to find Chaos, and made him his servant. As the story goes on, Eggman keeps feeding Chaos more and more Emeralds, until Sonic makes it onto Eggman's flying fortress the Egg Carrier, and defeat Chaos, knocking out the six Emeralds he had at that point. The Egg Carrier crashes, and Knuckles holds on to the Emeralds, thus ending the main story.

Final Story
Knuckles takes back all of the Emerald Shards, and the six Chaos Emeralds back to Angel Island, sending it back into the sky. As Eggman plots his revenge, Chaos finds and attacks him. Eggman flies to Angel Island to get Knuckles' help, but Chaos followed him and made quick work out of both of them. Sonic goes to see what is happening, and Knuckles tells him about Chaos' return. Sonic and Tails look for the final Chaos Emerald in the tornado, but Chaos gets to it before them.

Using the power of the seven Emeralds, as he did thousands of years ago, he becomes Perfect Chaos. He floods the city of Station Square, and starts attacking everything. Eggman, enraged that Chaos betrayed him, tries to use a new Egg Carrier to defeat him, but with a single blast Chaos rips the ship in two. Just when all seems lost, Tikal shows herself to Sonic, and tells him that they have to seal Chaos away before he could do any more damage. Sonic refuses, saying that if he is still angry it will just happen again. So, Sonic's friends gather the Emeralds, and Tails tells Sonic that Chaos only used the negative powers of the Emeralds, and that Sonic can still use the positive powers they posses. After this speech the Emeralds have their colors returned, and Sonic becomes Super Sonic.

After Chaos is defeated, he calms down, and returns to his more friendly nature he had before the shrine was attacked. Pleased, Tikal thanks Sonic, and she and Chaos return into the Master Emerald.

Sonic Generations
Chaos reappears only as Perfect Chaos in the Station Square as a major boss from the classic Sonic game, Sonic Adventure. He starts to go on a rampage. Luckily, Sonic didn't need to use the Chaos Emeralds to become Super Sonic and defeat Perfect Chaos. Sonic rushes and speeds up to Perfect Chaos's body, hitting his brain several times. After that, Perfect Chaos was defeated and sunken back into the water.

Sonic Forces
As shown in the E3 trailer for Sonic Forces, Chaos will appear once again and take the role of one of the main antagonists, along with Eggman, Shadow the Hedgehog, Zavok, Metal Sonic, and an new villain named Infinite.

Chaos 0
Chaos 0 is Chaos' first form, seen above. It is missing its tail (which had been swallowed along with a Chaos Emerald by Froggy), and possesses no Chaos Emeralds. This form of Chaos is considerably vulnerable despite its all-water composition, and can be defeated by striking its exposed brain. This form is fought only by Sonic in the beginning of his story.

Chaos 1
Chaos with one Chaos Emerald. This form only features minor changes from the first form. Chaos's head becomes broader and one of his arms becomes bulkier, developing a rigid endoskeleton (with the Chaos Emerald at the center of the "hand") and pincer-like fingers. This form is never fought, but seen after Sonic or Tails defeats Eggman the first time.

Chaos 2
Chaos's third form with two Chaos Emeralds is identical to Chaos 1, but now both arms are bulky and boney. This form is only fought in Knuckles' story, in the hotel.

Chaos 4
With four Emeralds, Chaos takes on a hunched dolphin-like form with a bony tail and fin-like protrusions in addition to his arms. He is found in the Mystic Ruins and can be fought with Sonic, Tails, or Knuckles.

Chaos 6
With six Chaos Emeralds, Chaos undergoes a much more dramatic change. In addition to becoming larger, Chaos becomes arachnid-like with several eyes and tendrils, and regains his true tail from Froggy. In this form Chaos also moves his brain to the center of his body, making him considerably harder to damage. He is fought on the Egg Carrier, and can be fought by Sonic, Big, or Knuckles.

Perfect Chaos
After absorbing negative energy from all seven Emeralds. Chaos 0 takes on an immense reptilian form, and gains several new powers. In this form, Perfect Chaos 0 can control far more water than before, and can create water tornadoes and fire lasers. This form was so powerful that he nearly managed to kill all the echidnas on Angel Island and flooded Station Square, leaving it in ruins. The form could only stopped by the power of Super Sonic, using the positive energy from the Chaos Emeralds against the titan. This form later returned in Mario & Sonic at the Winter Olympic Games during Sonic's version of Dream Figure Skating. The only difference is that it wasn't actually hurting anyone and was mainly just there to be a part of the show. He was also quite small and made of ice. This form is also fought as the second boss of Sonic Generations, fighting Modern Sonic instead of Super Sonic.

Sonic X
Chaos becomes the main villain in the Chaos Saga in the Sonic X anime. Much like the video game Sonic Adventure, Chaos was revived by Dr. Eggman and gets stronger with each Chaos Emerald he obtain. Chaos also takes on the same forms as the video versions such as Chaos 0, Chaos 1, Chaos 2, Chaos 4, Chaos 6, and Perfect Chaos. Much like his video game counterpart, the anime Chaos was defeated by Super Sonic.

Trivia

 * Perfect Chaos resembles Biollante from the Godzilla franchise.
 * It is implied that Perfect Chaos is the manifestation of the negative power of the Chaos Emeralds.
 * Chaos 3rd and 5th form were never shown in anywhere in the differing Sonic continuities.