A guardian of the master emerald and chaos emeralds, Chaos was a chao until he was exposed to emerald energy, making him the creature he is today
He is the main antagonist of 'Sonic Adventure',He appears in 'Sonic Adventure 2: Battle' as a playable character in the 2-player game modes.
Chaos is able to become pure liquid to avoid attacks and travel through tight spaces, he can also stretch out his arms to attack opponents from a distance.
When exposed to a chaos emerald, he can absorb it and evolve into a stronger form. The more emeralds he absorbs, the stronger he gets and more he evolves. When he has absorbed all 7 emeralds, he becomes perfect chaos, a monster who can project an energy shield, create tidal waves and cyclones of water, absorb projectiles and release them from it's mouth, and project a super-charged energy blast from it's mouth.