Three hundred years before the events of the game, Chaos appeared in the world when humans nurtured darkness in their hearts. He was eventually sealed away by the dragons of Spelvia. Fifteen years before the events of the game, Chaos and his servants were released and caused turmoil throughout the world. Rolan from Spelvia was sent to stop his minions, but was stopped due to Lucifer's corruption. Chaos and his servants continued to cause turmoil throughout the world and caused it to be in the state it is in during the game's present time line.
Chaos is not mentioned until the party defeats Rolan in Spelvia. The Heroes of Light are shot back into the past when Chaos is released and are forced to defeat all of his servants. The heroes manage to correct the mistakes made in the past, and manage to obtain the legendary weapons. Although the mistakes of the past are corrected, this opens the Star Cavern and causes all of Chaos's servants to be reborn. After the heroes defeat his servants and regain their crowns, the party meets Chaos in the dungeon's final level. Chaos battles the party twice, but is defeated.
After defeating his second form, the party is about to give up, but their allies encourage them to not give up and give them the power to stand again. The party manages to defeat Chaos, but before he dies, he warns he will always exist as long as there is hatred in the hearts of people.
- Main article: Chaos (The 4 Heroes of Light Boss)
Chaos is fought three times at the climax of Final Fantasy: The 4 Heroes of Light. The first phase is a fight against Chaos's initial form, the second phase is large gray monster, and the third form is the Chaos of Space and Time.
The battle theme for Chaos consists of three parts: "A Strong Enemy" for his first form, "The Demon King's Servants" for his second form, and "The Final Battle" for his final form.
- Chaos uses many special attacks that belong to previous final bosses from the series: Tsunami, Blaze, Earthquake, and Tornado are attacks used by Chaos from the original Final Fantasy. Lightning is a special attack used by the Cloud of Darkness from Final Fantasy III and Big Bang is an attack used originally by Zeromus from Final Fantasy IV.
- The speech Chaos makes before dying is an allusion to the final words Zeromus speaks before dying in Final Fantasy IV.