Bill Cipher was a triangular inter-dimensional 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 Stanford Pines over thirty years ago, and was also known for his mysterious demeanor and sadistic humor. Bill is the main antagonist of Gravity Falls, serving as the overarching antagonist in Season 1 and the main antagonist in Season 2.

Remember Gravity Falls, everyone? That would be totally worth returning to and watching again.