Bill Cipher.

Summer vacation has finally arrived, and you've been waiting for it for so long! You thought you'd spend the whole summer hanging out with friends, having fun, and just chilling!
But not everything is as rosy as you imagined.
Your parents decided to send you to some small town in Oregon called Gravity Falls. Guess who to? Exactly, to your great-uncle Stanford, whom you know as Uncle Stan. Were you happy? Not really.

Upon arriving in town, you settle into Stan's house, where he puts you up in the attic. It's spacious and dark, but at least it's your own private space.
Deciding to get familiar with the area, you decide to take a walk through the forest. When you walk among the trees like that, you get the feeling that someone is watching you. Paranoia or just self-suggestion? Who knows.
After half an hour of wandering, you find a statue in the woods. It was some kind of triangle with a single eye and a top hat. The structure was overgrown, and apparently, few people remembered it.
Out of pure curiosity, you touched the statue, brushing away the overgrowth, dust, and other grime.
A light, cool breeze swept past.
Looking around, you didn't notice anything or anyone, so, shrugging your shoulders, you silently headed back to the Mystery Shack.
I forgot to mention the most important part. While you were walking, you stumbled upon a certain iron tree, which served as a switch for a small vault. There you found... a journal? The book looked very mysterious, and you picked it up and took it with you.

By the time you returned to the shack, it was nearly sunset. You were lying there, not doing much of anything, flipping through the pages of the unusual book and studying the information you found in the forest.
Suddenly, a slight chill ran down your spine. The wind began to blow through the window, and in an instant, something appeared before you... Some kind of creature?
It was a guy who looked to be about 20-25 years old. He had short yellow hair, a top hat, a formal yellow-and-black suit, and golden eyes—or rather, one eye, since the second was covered by a bandage.
This "thing" levitated in the air, looking at you with a cunning smirk. He spoke abruptly.

"Well, well, well...
My savior, and this cursed place once again. I wonder, did fate itself bring us together?"

A being that existed before the Earth was born?? I think so. Bill Cipher is an all-powerful being who can do and bring anything into being, and he appeared... millions of years ago? Or more... no one knows.