When the universe began, there was nothing. Just an infinite void, not even a molecule of gas to exist within it. Gradually, over a seemingly infinite time, matter was created through quantum vacuum fluctuations *Actual possible explanation for Big Bang matter*. This eventually coalesced into a being simply called "The First".
The First could be equated to god, but that would be a bit misleading. This being was not timeless, spaceless, all powerful, or even all knowing. It was only one thing: curious.
With the time it had, The First experimented with the excess matter around it, creating the many other elements.
As it's experiments continued, it learned of all the rules and processes of the universe it lived in.
And then... It was bored.
As a way to alleviate it's boredom, The First created The Second.
And it was happy.
The First gradually taught The Second all it knew, and then they both knew all the rules and processes of the universe.
And then they were both bored.
So, The First made The Third and The Second made The Fourth.
This process continued until there were so many primordial beings they filled the infinite universe.
And they were all bored.
As a final measure to stop the boredom, The First came up with an idea.
Rather than teach all there is to everyone, there would be a barrier to all knowledge they wouldn't pass. This idea came into fruitition when it created The Veil.
With The Veil in place, all the beings would lose their infinite knowledge.
But there was a problem with that: They could simply relearn everything.
To stop this, The First also created what we today would call a "Dimension".
The first of its kind, this dimension was able to sustain basic organisms that could evolve and reproduce, but shortly after die.
This wouldn't entertain them, and The First knew this, but it was merely the first step of his plan.
Whenever something died in this dimension, it was sent beyond The Veil, granting it infinite power and knowledge over a new Dimension.
From there, the being could either join a dimension that already existed, or make their own.
With infinite beings, there comes infinite dimensions.
And they were happy.
Unfortunately, with every variation of every Dimension, some dimensions would naturally destroy others.
Having predicted this, The First had two final tasks to complete. The first of these: Create a space between the dimensions in which you technically exist within them all: The dimensional gap. Second: Create something to replace the destroyed dimensions.
The second goal took a little more effort. The issue of boredom came about because the primordial beings could know all, and as such this new being couldn't have this ability. As such, the newest in lines of super-beings, was given truly infinite power but not infinite knowledge.
The being's name was Ophis. Unfortunately, Ophis had other plans, and went off into a dimension of it's choice to do god knows what.
Realizing his mistake, The First makes another one, this one called Great Red, with a strict limitation that it couldn't actually enter a dimension, but rather eternally wander the dimensional gap.
Great Red's job was to stop the ripple effects Ophis would cause which would lead to a devastating calamity across the dimensions.
Unfortunately, it wasn't enough. In one dimension a certain God Dragon mated with Ares, spawning the true successors to the destruction of reality: Iroas and Irios.
These beings, automatically feared for their world-ending power, were sealed away in the dimensions version of Tartarus, but it wasn't enough. They eventually broke free, and they were going to destroy everything.