Many, many, MANY eons ago, God created The One. He gave this soul the power to do as it wished, with only one responsibility.
Alleviating his boredom.
So it created the system, a series of hallways which intertwined every conceivable alternate reality called the Nexus Halls.
It chose to pull one human from each reality at random, since humans were God's favorite creation, and place them in the hallways, opening up infinite possibilities. All of these humans were granted a choice in the form of two doors, which could lead to any number of places.
God was no longer bored, and the chosen humans quickly grew in power achieving godhood and more. The strongest of these humans-turned gods were known as the Celestials, of which there were eight.
The leader of these celestials was known only as Timmy, and Timmy was the strongest of all those chosen by The One. Until a boy named Jack was chosen.
Jack was different from all the others chosen so far, he had more potential than any yet, and he quickly grew in power.
Quicker than even the Celestials. Timmy was threatened by this. So he sent his apostle after Jack. When he defeated his apostle Timmy came after Jack himself.
Jack and Timmy's battle lasted for days, the celestial eventually coming out on top. Thinking Jack was helpless, he went into a monologue explaining Jack should never have threatened his rule, yada yada.
But Jack was not helpless, he ended his own life. But the chosen have both a blessing and a curse, immortality. Forever destined to return to the Halls.
After Jack recovered, he gained allies, grew in power, and struck back against Timmy. The celestial subsequently lost, and Jack took away his powers and left him stranded in a deep dark corner of reality for eternity.
Jack grew even more after that, becoming so powerful he gained God's direct attention. He fused The One with Jack, creating the ultimate entertainment.
Jack also became bored. He had stopped growing, stuck at only a tenth of the power of God. He started sharing power with other Chosen, hoping that they would be able to grow as strong as he did. But none were able to. They all fell into Chaos.
So he gave up, letting the system choose randomly who to give power to, and eventually granting power to a boy.
A boy named Eric Steel.