Chaos

is an impure and pure entity of darkness that even the Demons feared and light that even the Goddesses worship.

Personality
Nothing is known about its personality, except that it was disappointed with it's creations prior to creating humans, due to them not living up with its expectations yet saw humans, despite being incomplete and much more fragile and short-lived than the other races, as it's greatest creation due to being the closest race to mirroring Chaos.

History
Said to be born amidst ancient stars that were very far away, Chaos first created the world, then it bore that Supreme Deity, the Demon King and later the Sacred Tree. After that, it created the fourth race, the Giants. Chaos was disappointed with them because they were a savage race, slaves to their power and knowing nothing other than inflicting pain on each other. Then it created Humans, kindness and malice, bravery and cowardice, love and hatred, beauty and beastliness. Although incomplete, they were the perfect race that came closest to it. The Supreme Deity and the Demon King were filled with jealousy and apprehension of Chaos, fearing that the love and respect that their own races had for them, would be stolen by their own creator. Thus, the two gods joined together and sealed Chaos away, allowing them to be the two rulers of the world and believed to be the most powerful entities in existence.

Abilities/Equipment
Chaos is shown to be a extraordinary powerful being, as it created the Supreme Deity, the Demon King and the Sacred Tree from nothingness, and the three in turn created three of the most powerful clans in the world and three separate dimensions to inhabit and live in.

It required the combined godlike power of both the Supreme Deity and the Demon King to seal it away, making it the most powerful known entity in the entire world of Nanatsu no Taizai.

When Arthur became the "King of Chaos", he was able to use the power of Chaos to deform reality.

Trivia

 * Chaos is likely based off the concept of the same name from Greek mythology, said to be a void state that existed before the world itself and was said to have spawned the greek gods from nothingness, similar to how Chaos did the same with the Supreme Deity and Demon King.