Khaos is the physical manifestation of all negative emotions.
He has no true physical form or body, instead he has the ability to possess another persons body when they are filled with enough negative emotion such as rage, fear, envy, or greed. He can influence human thoughts and emotions and trick people into doing terrible things as a source of power and sustenance for himself.
When the cycles of time shift toward the dark Khaos always attempts to destroy the light and conquer the universe. This gave rise to the need for a saviour to help Gaya protect the light energy and keep the cosmic scales balanced as the cycles of time change again and again.