Bill Cipher is a two-dimensional interdimensional demon, formerly existent only in the Mindscape before succeeding in gaining access to the real world. He had been running amok in Gravity Falls, Oregon since being summoned by Ford Pines over thirty years ago. Known for his mysterious demeanor and sadistic humor, Bill is the overarching main antagonist of the overall series. 

Bill is a yellow, sometimes multi-coloured, two-dimensional and triangular creature that bears a strong resemblance to the reverse side of the Great Seal of the United States, which in turn consists of the Eye of Providence and an unfinished Egyptian pyramid. The color of his body briefly becomes lighter when he speaks. Often when he appears, the area he appears in takes on a washed-out monochrome appearance. It is unknown whether this effect physically occurs, or if it is simply a visual effect to bring attention to his appearance