Before the creation of the universe, there were 2 entities that constantly battled; The Ultimate and the Eternal
The Ultimate was a vaguely humanoid shaped being, though it had a tail and was completely black and glowed with a white outline
The Eternal on the other hand, was a giant planet sized monster, with dozens of large tentacles and a giant mouth in it's center with rows of sharp teeth and a single slit eye in the middle

(this art is old but it's the only thing I have for now...)
One massive clash between them created the universe and it began to rapidly expand
During one of their battles, the Ultimate was beaten and tossed into some area of the universe called the Milky Way. It then needed time to recover, pulling loads of rocks towards itself to hide from the Eternal
After a few billion years, the Ultimate was finally ready to emerge from the giant celestial body
It had watched life arise from the ocean and took a keen interest in humankind, though it sensed the horrific violence and suffering of human wars, corrupting it's mind. It finally emerged from the core of the Earth, though it had taken a physical body which reduced it's power significantly and was now filled with evil intent. This new entity traveled across the planet, tormenting humanity and causing countless to suffer. This demon was eventually sealed away after a few hundred years, the seal stayed intact for thousands of years, until it began to crack...
There's part 1 of the yap sesh on his backstory, just taking a break right there in case you have any more questions unless you'd like me to continue :)