My First Emoji I Think We All know  wo this is sigma

Bill Cipher is the main antagonist of the animated series Gravity Falls, a chaotic, one-eyed, triangle-shaped dream demon who desires to bring chaos to the third dimension. He originates from a two-dimensional world called Euclydia, which he destroyed after developing the ability to see the third dimension and seeking power. He can invade minds, cause madness, and has a specific goal of merging his "Nightmare Realm" with the physical world.