Basically the previous 4 knights knitted together.
Before anything exist, before the concept of existing itself is void, there's nothing. Just an empty void of nothingness. There's only a being. A form of consciousness. This consciousness began create life, when life born, new concepts arise, and a new balance was created.
The consciousness also create more and more existence, but from the existence so born the non-existence, aptly called Chaos. Physical incarnation of the concept of non existence. That is Chaos Knights. They goes by many names and forms in various perspectives. But the one thing that always the same, their power are power that defies existence. As long as there's something exist, even the faintest existence, they too will always exist. Thus, their immortality is something that even Heaven and Hell cannot comprehend. The Chaos Knight itself already exist even BEFORE Heaven or Hell were there.
Initially, they were mere tools. No will of their own. They exist only to end all existence. The ultimate enders of all. They are not evil, neither they are good. It is their purpose. It is their function. Remorseless and heartless, they are no different then machines programmed to do whatever it was told to do. That was, until the creation of humans come to play.
In a small twinkle of perhaps mischief, the consciousness, unianimously regarded as the One by the Chaos Knights, put their souls and compressed all their world-ending power into human flesh. This act was not without reason. The One wanted to at least, taught these knights of Armageddon what it means to feel. The One also erase their memories, making them forget who they are as a precautionary measure.
The Chaos Knights' human incarnations had always follow a certain sequence: At the age of ten, their Chaos power will surface for the first tme. Then, through a period of time, it will grow stronger and stronger, changing the human's personality to close of that of the original Chaos Knight. Every human incarnation they choose turn out no different then the original: heartless, cruel, and in some instances, lunatic.
When the human reached the peak of their power, they stop aging, and unable to be killed except by another Chaos Knights. However, they are now mortal. The human body they used are subject to Chaos' overwhelming power. As time went by, their body will destroy itself, unable to contain the inifinite Chaos power, the process which took centuries, and finally, they will die. A weakness they contracted when they enter human body. Given that now they have fleshling bodies, the Chaos power exercise a certain limit to how much power it can exert. As the result, they lost much of their once invincible destructive capability. Another drawback they all share.
Yet, the One continued this tradition, gambling in the small hope that one day, in one incarnation, there will be one strong enough to fought the Chaos impulses, and the Chaos Knights will refuse to destroy the world. For that is what needed to end the world: the four knights must be present at the same century, and all four knights must be WILLING to destroy all. A condition that has yet to be met, prolonging the universe' existence for countless eternity, much to the One's delight.
However, as generations after generations of Chaos Knights went, better, stronger bond between the Chaos Power and the human body are forged. The Chaos Knights began to regain their former power and Immortality. Then again, the human race itself had also shown increased quality and resistence to the impulses of the Chaos Power. With each generations, the Chaos Knights becoem more and more, as the One wish it, humane. Yet, none of them show any signs of defying their fate, but so far, they destroy just because they must, not because they want to. It wasn't until Fllahn's generation that the One finally have its wish: Fllahn, the Lord of War, REFUSED to destroy the world. A Chaos Knight finally rebelled againts its own purposes.
Meanwhile, Heaven and Hell, the domain that ruled the world at the time and in endless war between each other, responded Chaos Knights existence with different reactions:
Hell wants them.
Most of the Heaven despise them. Only some sought to protect them from Hell.
And with the other three are ready and willing to destroy everything, Fllahn decision hangs the universe' fate on a single thread of hope...