@CrimsonFenrir7
Basically, long ago The Backrooms was known as Magnae Terrae, and it was being ruled by a demon-like king. A bringer of hope known as Casador defeated him but because the lands were too harshly poisioned by the king some people of the land turned into Entities. The remaining people and Casador traveled to a far-away land that was safe, and that's where they are to this day.
But the demon king, also known as Anguro, is still hiding in the Backrooms, waiting for a moment to reveal himself.
That's the backstory, or at least as much as I will tell you for now. I don't want to tell you everything already.