At the very least, we all have a general understanding of It. It lives in the macro verse (also known as Todash Space in the Dark Tower books), which surrounds all universes. It came to Derry before humans came to North America, maybe even before humans actually existed, and eventually gained an iron grip of influence and control of Derry, Maine. It can take the form of any individuals worst fear. It likes to take the form of Pennywise the dancing clown, and this physical aspect of It (the one that can shapshift and confront the Loser Club) exists as an extension of It.
But the part of It that most relates to my theory is this-It believes that the only two supernatural beings in existence are Itself and Maturin the turtle. It begins thinking there might be an other being, but died before making up It's mind. So my theory is that It didn't exist until after Gan created the Dark Tower, that It is some form of demon that is still actually very VERY young, considering It calls the turtle old and stupid like some kids would talk about certain adults. So the reason why It isn't aware of other beings like the Crimson King, Gan, or even Walter is because It is still very much a child and hasn't existed long enough to learn about anything relating to these figure.
But the part of It that most relates to my theory is this-It believes that the only two supernatural beings in existence are Itself and Maturin the turtle. It begins thinking there might be an other being, but died before making up It's mind. So my theory is that It didn't exist until after Gan created the Dark Tower, that It is some form of demon that is still actually very VERY young, considering It calls the turtle old and stupid like some kids would talk about certain adults. So the reason why It isn't aware of other beings like the Crimson King, Gan, or even Walter is because It is still very much a child and hasn't existed long enough to learn about anything relating to these figure.