Chaos King was created so that chaos could enter the universe, if he dies nothing can ever move again. When he got his form he went to earth and met Shadow and Zanabel. He eventually became Shadow's enemy but got destroyed in their final battle. His soul and mind survived and possesed Newlee.
Chaos King was created so every living thing would be supplied with Chaos Energy. It is unknown who created him, but they thought he didn't have a will of his own. His body was split into two parts and they both became legends. One used Chaos to make things, the other used chaos to destroy things. Chaos King patrolled the galaxy looking for them and found them fighting and absorbed him. He finally got form and went to earth. When he got to earth, Shadow and the others were fighting against organization XIII. He joined the battle and helped defeat them. During his and Shadow's adventures and fights, Chaos King develops a hate for Shadow because of his power. Eventually he challanged Shadow to a duel. During the duel, he destroyed Omega with the Ultimate Chaos Blast. He then breaks Shadow's Berserker sword I. Shadow absorbed the sword and went into True Techo form. Chaos King put them into an explosive chaos void at full power and used the power from it to do an Ultimate Chaos Blast at full power. However, Shadow coutered it and destroyed Chaos King. However, Chaos King's spirit survived and possesed Newlee. Eventually, Newlee got him out. Chaos King manifested himself as a copy of Newlee and fought Shadow and Newlee. Shadow defeated him with a new technique, but almost died in the process. Newlee then trapped his spirit in Neb's sword. When Shadow died, it went after his spirit. Eventually, Shadow came back to life and tricked him and sent him into a box. His spirit went underground and started to wreck havock on earth. He got Xion to let him possess him. He went out of Xion and almost killed Shadow, but he got powered up and obliterated Chaos King's Soul with a new technique. Chaos King still exsists in other dimensions.