Chaos King

"It has no form, no shape, no nothing. It's simply Chaos. I know it's hard to believe, but that's how it is: chaotic. It's its very nature, after all."

- Ethan Milani. Chaos, also known as Khaos, was the first ever deity to come between the primordials, and gave birth to all of them. Although some may think Chaos is both Chaos, the deity, and a shapeless void below the depths of Tartarus (just like Tartarus himself is both a place and a deity), it's been proven more than once that, like its son, Chaos is able to create a physical body which is by itself very hard for both humans' and deities' eyes to understand fully. As such, most people will see Chaos as a monstrous, human-like creature.

Beginning of Creation
Chaos was the initial state of the universe before creation; a gloomy, soupy mist containing all the matter in the cosmos. Eventually, it somehow grew to a sentient being. Growing tired of its own cosmic loneliness, some of it collected to form the Earth ( Gaea ), the Sky ( Ouranos ), the Seas (Pontus), and the  Infernal Pit  ( Tartarus ). Later, Night ( Nyx ) would also be born from Chaos in union with Tartarus. The universe was born.

Hera's Punishment
After beginning an Olympian riot against her husband  Zeus ,  Hera  and the other  gods  were punished for their rebellion. While  Apollo  and  Poseidon  were temporarily stripped of their godly powers, Hera was given the worst punishment of all: she was chained right above the terrifying abyss of Chaos. Every day, Zeus would visit his wife with the  Master Bolt  and threaten to let her tumble into the void. Hephaestus  could hear the wails of his mother all the way from  Mount Olympus, which infuriated him, as he could not bear to hear her suffering such a harsh punishment. As a result, he finally set her free. Hera tearfully embraced him, and promised to never to call Hephaestus ugly ever again.

Guardians of Chaos
As it became once again tired of being alone, since most gods, even the Protogenoi, were too afraid of its power to actually try and enter its realm, Chaos disguised itself as another of Hades' dead souls and went to the Underworld. There, it couldn't really understand what it witnessed. Never having been introduced to such concepts as good or evil, Chaos had no idea what it meant to be taken to the Fields of Punishment or the Elysium, and as such couldn't possibly know that it shouldn't go and take some of the souls in an attempt to better understand the world. From its many interactions with those in the Underworld, Chaos would eventually come to believe it was its duty as the creator of the universe to make sure the universe would be fine, and the only way to do that would be not by destroying the evil or good side, but to try and keep the balance between them. In order to help him to do that, since Chaos realized its very presence was something to big for the universe to be able to withstand for much longer, it ultimately created the Guardians of Chaos from those who he considered to be friends between the souls inside the Underworld and gave them the task of making sure balance wouldn't be corrupted.

Meeting Eetion Mathéos
Eons after that, Chaos would eventually come to know Ethan Milani after Persephone, who hated him for being the son of Hades with a mortal woman, threw the son of her husband into Tartarus. And he was different. Unlike most gods and most of its guardians, Chaos realized Ethan was not afraid of talking his mind to Chaos, a trait the primordial deity greatly enjoyed. With Ethan's help, Chaos would develop a better vision about the world it had created eons ago, and what it came to know fascinated Chaos, which wanted to see it by itself. So the Protogenos created its first actual corporeal form -- a scary, human-like monstrous creature with milk white skin, no mouth, eyes, hair or anything else, and several tentacles on its back, which Ethan described as a "pure mass of primordial chaos shaped by force into a human-like body, incomprehensible even to the eyes of the gods". It would eventually become Chaos' most used form when taking a physical shape, since it's easier to shape into. Ethan would eventually grow to become Chaos' most trusted guardian and thus its lieutenant.

The Guardian of Artemis
(As of May 03, 2017, Chaos has yet to be seen in TGA series.)

Appearance
"A pure mass of primordial chaos shaped by force into a human-like body, incomprehensible even to the eyes of the gods. It's not its actual form, neither it is how Chaos has actually shaped itself, but it's the best our eyes can show us without our minds shattering. There are some things in this universe which aren't meant to be seen or understood."

- Ethan.

Abilities
A s the first of the Protogenoi,  Chaos is immortal and has existed before the world began. He is also the creator of the other Protogenoi and thus the creator of the universe, since the other Protogenoi are the parts of the universe itself. Chaos is believed to be one of the few things, able to truly kill an immortal being by absorbing its essence. As the creator of the universe, Chaos is also an immensely powerful being. It has been shown powerful enough to mind control Olympian gods even without meaning to, just by asking them to do something -- which seems to bother Chaos, since it can hardly have a true conversation with another being, even a god, because they're usually too afraid of him to say what they actually think. When angry, Chaos' very presence is enough to weaken another god, even another of the Protogenoi, to the point they are temporarily forced into a human-like state, similar to how Chaotic Silver acts when used against a god, but to a much higher degree. Some have even stated Chaos to be an omnipotent being, though it is a very unlikely thing according to its Guardians.