Bill Cipher

Bill Cipher is the main antagonist of the 2010s TV show Gravity Falls. The creator of Gravity Falls, Alex Hirsch, is his voice actor. Bill is a yellow demon in the shape of a triangle, who can invade people's dreams. He appears to the characters of the show for the first time in the episode "Dreamscaperers", but he has been hidden everywhere throughout the backgrounds and environments of the show, including the opening theme. He originates from Euclydia. Euclydia is a fictional 2-D dimension that has since been destroyed. As told in The Book of Bill, Bill destroyed his home dimension by accident, because he tried to “free” them and help them see the third dimension, or in his words “see the stars”. Bill is a chaos demon, with his only goal being to cause pain and weirdness to all. Long before the events of the show, he and Stanford Pines were friends, until Stanford's research partner, Fiddleford McGucket, got a glimpse of Bill's true plans.