Bill Cipher

The Big Bad from Gravity Falls is Bill Cipher, a Mad God from the Nightmare Dimension that takes the form of a triangle with a single eye, a hat and limbs. He is revealed to be the Greater-Scope Villain behind the mysterious journals that drive the main narrative, the books having been separated and hidden to prevent Bill from entering the waking world and bringing about Weirdmaggedon. His image can be found all over the town, Word of God stating that this is how he is able to keep an eye on the events that goes on there.

Example of:
Eye of Providence