Bill Cipher (voiced by Alex Hirsch) is the main antagonist of Gravity Falls. He is a triangular dream demon formerly existing only in the mindscape who wished to gain access to the real world. He has been running amok in Gravity Falls, Oregon since being summoned by Stanford Pines over 30 years ago. He is known for his mysterious demeanor and sadistic humor. His plan was to spread was to spread chaos all over the world once he gets to the 3rd Dimension, but in the end he was defeated when the Ford twins switched places, making Bill to go into Stan's mind instead of Ford's mind. Once he was in the mind of Stan Pines, Mr. Ford used the memory erasing gun to erase Bill out of existence.
- Bill Cipher appears in a epilogue of Jeffrey, Jaden, Hiccup & Juniper Lee's Storm Adventures of My Little Pony: Friendship is Magic - To Where and Back Again.
- Bill Cipher will become Jeffrey, Jaden and Hiccup's enemy in Jeffrey, Jaden, Hiccup & Friends meet Doctor Strange.
- Jeffrey, Jaden and Hiccup will face Bill Cipher again in Jeffrey, Jaden, Hiccup & Friends go to Gravity Falls.
- His design looks like the eye of the pyramid on the back of a dollar bill.
- Bill Cipher will make his debut including his laughter in the end of Equestria Girls: Legend of Everfree, where he is released from the Wondercolt Statue after Midnight Sparkle destroyed it during battle by the events of Equestria Girls: Friendship Games.
- Bill Cipher will become the Rainbooms' enemy in crossover of "Equestria Girls: Mirror Magic".
- Twilight, Sunset, Kyle, The Rainbooms and The Z Fighters will face Bill Cipher again in The Rainbooms & The Z Fighters go to Gravity Falls.
- In the series, Grim is aware about Bill, saying they two have went WAY back in the centuries and used to be partners along side Anubis, and explaining his fellow Rainbooms that Cipher is not only a Dream Demon, but also known as the "devil of all the reality and multiverse" as well as the "father of demons".
- Bill Cipher will be resurrected by Mandrake to join his kingdom.