Chaos is a Chao that mutated into a water elemental, which was responsible for all but wiping out the Knuckles Tribe of Echidnas. Imprisoned in the Black Emerald by Tikal, a girl from that tribe, Chaos remained trapped for centuries until he was released by the maniacal Dr. Eggman. After accumulating power from various Super Emeralds, he attacked Station Square only to be stopped by Super Sonic. Following this, Chaos, Tikal and the Seven Server Chao he where protecting returned to their zone within the Black Emerald.