Chaos is a powerful ancient water-based creature from the Sonic the Hedgehog series, most prominently appearing as a major antagonist in Sonic Adventure. Originally a gentle guardian of the Chao, it was transformed by suffering and the misuse of the Chaos Emeralds into a destructive force. Chaos serves as a central threat in the story, especially in its Perfect Chaos form, and is closely tied to the lore of the Master Emerald, the Chao, and the history of Station Square.