In the Beginning...

IN THE BEGINNING there was nothingness upon the deep, no stars or suns; no planets or universes.
Light existed in great abundance, beyond the ability of mortals to fathom the size and dimensions thereof. So, too, existed darkness.
The two existed in harmony for eons upon eons, though time had yet to be measured at that point.
Eventually the two developed consciousness. For a while, things went well; the light and darkness were friendly toward each other and helped each other out as they became used to being self aware.
While Light continued to do well, dark began to slip into fitful fancies and the two began to fight.
During one such fight, the fabric of everything around them and they themselves became torn apart and from that tear stemmed all life as we know it.
Scientists have theorized that this was the Big Bang; Religions stake their claim that this was God and the Devil. While both adequate descriptions, they do little justice to the truth.
These were not Gods, though they are immortal. They are not perfect beings, though some times they seem as such when viewed with mortal eyes. They had no real knowledge of mortal or even material beings until quite some time after they accidentally created all of what we know.
In fact, what we know isn't even what we think it is. This is the third or fourth or fifth reincarnation of everything we know. When Light and Darkness fought and torn a hole in everything, they created a chain of events that is doomed to repeat itself every so many eons. All universes exploded outward of countless sources and they continue to spread outward at the same time as being drawn back into those sources.
Upon the accumulation of everything drawn back into the sources; known as black holes; the black holes then begin to combine to create a semblance of the world that Light and Darkness existed in before the tear and once they gain enough mass within them; explode outward again.
But this does not repeat life forms, just restarts life in general. There is no guarantee that we will live again when everything comes round again. We already live alongside of countless alternate realities where all of our choices are mapped out.
Light and Darkness continued to fight even with the destruction of the cosmos reigning down upon them, until one of them realized that life was growing on the little rocks that were shooting through space and through them.
They fought battles over these lives. Some times Light would win and they would be saved and some times dark would win and the people would lose; but all over they continued to cause destruction until finally Light turned to Dark and called for a truce to declare conditions for a game they could play for the rest of eternity in lieu of trying to destroy what simply could not be destroyed. They would make bets and play games of subtlety with the lives of mortals.
This appealed to darkness because it could then spread dark thoughts and animosity through people over time and slowly and torturously tear apart everything they knew and drag down the best of them all and leave them as nothing. Light knew that while they played the game, there was chance to save more lives than by simply fighting. Light could understand things that Dark could not and vice versa. Whereas outright fighting destroyed nearly 75% of all life that existed, Light could save at least 50% of life by engaging Darkness in the game. Over time, they've only gotten better at their respective roles.