- “Do you have ANY idea what I'm like...WHEN. I'M. MAD?!”
- ―Bill Cipher when he's mad
- “Name's Bill Cipher! And I take it you're some living ventriloquist dummy? Haha! ”
- ―Bill Cipher to Lil' Gideon
Bill Cipher is a psychotic inter dimensional Dream Demon and the true main antagonist in Disney's Gravity Falls, serving as the secondary antagonist in Season 1 and the main antagonist in Season 2.
Bill originates from an alternate 2-dimensional universe which he "liberated" by plunging it into a flaming chaos, effectively destroying it and all of it's inhabitants. After destroying his home dimension, Bill fled to an unstable, boiling, inter-dimensional crawlspace called the Nightmare Realm where he learned he had to merge the realm with a 3-dimensional universe in order to prevent the lawless subspace from collapsing in on itself.
Without a physical form, Bill was forced to access this 3-dimensional universe through the mindscape, attempting to manipulate it's inhabitants through their dreams. Such victims of Bill include the Ancient Egyptians, George Washington, and Stanley Kubrick, all of whom failed his orders and were punished by eternal nightmares.
During the late-20th century, Bill manipulated a genius scientist named Stanford Pines into creating a portal to the Nightmare Realm in a secret lab found within the town of Gravity Falls which served as a magnet for that universe's supernatural occurrences. Bill lied to Ford, telling him that he was a muse and that the portal would benefit mankind and in exchange for his guidance, Stan allowed Bill to take control of his body while he slept, but after Stan's assistant Fiddleford McGucket witnessed the horrors that laid on the other side, Ford decided to shut down the project only for Bill to try and rebuild the portal as he slept. Knowing he had no other choice, Ford destroyed the portal and hid the blueprints in three different journals, two of which he hid in secure locations, the third he asked his estranged twin brother Stanley to hide only for a fight to break out between the twins which unintentionally caused Ford to get sucked through the portal.
In an attempt to retrieve his brother, Stanley took on his identity and turned Ford's cabin home into a tourist-trap to pay the bills while secretly hunting down the two missing journals and rebuilding the portal in his free-time.
He debuts in the episode: "Dreamscapers", where he was summoned by Lil Gideon to invade Stanley Pines' mind and the steal code to Stan's safe, so Gideon can take over the Mystery Shack. Bill fails at this attempt and tries to kill Mabel and Soos, but Dipper is able to defeat him, causing Bill to retreat and spare Dipper and the other's lives.
He reappears again as the main antagonist in the Season 2 episode "Sock Opera" where he possesses Dipper's body (called Bipper) and tries to talk Mabel into giving her the Journal or else he'll kill her by dropping her off the stage, but Mabel is able to avoid this and defeat Bill and get Dipper's body back, Bill get's into a body of a puppet. While in it, Mabel turns on the fireworks, which sends Bill back in the mindscape.
He also appears in "The Last Mabelcorn", were he tries to convince Stan's twin brother, Ford Pines to let him out of the Mindscape, but to no avail. He then looks for another host outside of the Mystery Shack as a result of a dream barrier put around the Shack.
In "Dipper and Mabel vs. the Future", Bill possesses Blendin Blandin's body and successfully convinces a heartbroken Mabel to destroy the time rift, as everyone was too busy to celebrate her and Dipper's 13th birthday. Bill then manages to merge the mindscape with the real world, putting Gravity Falls into a post-apocolyptic state and putting Mabel in a comatose state.
In "Weirdmageddon: Part 1", Bill and his demon lackeys (which he refers to as his "henchmaniacs") terrorize Gravity Falls and turn almost every citizen (including Ford Pines) into stone, in use for his throne room in his headquarters known as the Fearamid. Bill then imprisons the unconscious Mabel in a dream prison and annihilates Time Baby so that nothing stands in his way.
In "Weirdmageddon: Part 2, Escape from Reality", Bill realizes that neither he nor his henchmaniacs can get out of Gravity Falls due to a barrier preventing Bill's worldwide chaos from expanding. He then plans to unfreeze Ford to get the information out of him. At that same moment, Dipper and the other manage to free Mabel and convince her to come back to Gravity Falls.
In the Season 2/Series finale episode "Weirdmageddon: Part 3, Take Back the Falls", Bill unfreezes Ford and painfully forces him to give out the info on how to remove the barrier, which Ford refuses to do. Dipper, Mabel, Stan, and the other surviving citizens band together and create a giant mech to fend off Bill's henchmaniacs and Bill himself, while Dipper, Mabel, Stan, McGucket, Wendy, Soos, and Pacifica parachute over to Bill's Fearamid to rescue the citizens. After Robbie, Ford, Gideon, and the others are freed, Ford draws the circle from the series and tells everyone to step on their remaining symbols to destroy Cipher, but Stan refuses and both him and Ford get into a fight, ruining the plan. Bill then immobilizes the mech after finding it's weak spot, and turns everyone but the Pines family into tapestry banners for his Fearamid. He then imprisons Ford and Stan, turns into a monstrous creature, and chases after Dipper and Mabel throughout the Fearamid. The younger Pines twins are eventually caught by Bill and are about to be killed, until Ford convinces Bill to spare the kids and go to his mind instead. Excited, Bill's physical form turns to stone and his dream form goes into Ford's mind, only to find out that he is in Stan's mind instead of Ford's. Turns out, Stan and Ford switched clothes and tricked Bill into going in Stan's mind. Ford reluctantly sets the Memory Gun (from "Society of the Blind Eye") to erase Stan's mind, and traps Bill in Stan's mind as the dream Shack bursts into flames. Bill desperately tries to plea for his life, but Stan refuses, as Bill messed with his family. Bill's body starts to glitch and get distorted as he makes one last attempt to kill Stan, but Stan manages to obliterate Cipher with one punch, destroying him for good and sending his henchmaniacs back into the Mindscape. Eventually, Stan's memory is restored, Gravity Falls is back to normal, and what is left of Bill Cipher is a lifeless statue.
- He is based off the Eye of Providence and Mr. Peanut.
- Bill Cipher's first name is an allusion to how the Eye of Providence is found on the dollar bill.
- His first name is an allusion to the Beale Ciphers.
- His last words when reversed are: "A-X-O-L-T-L! My time has come to burn! I invoke the ancient power that I may return!". This indicates that Bill Cipher may be brought back or something, which has not been confirmed by the Gravity Falls producers.
- During season 1, Gideon was the villain and Bill was just a reccuring figment, until his major role in season 2 where it is revealed that he was only using Gideon for his benefits, making him in fact the true villain.
- Bill makes a cameo in the seventh episode of the second season of the Adult Swim series Rick and Morty where he is seen on a monitor in an alien couple's counselling facility and Bill's voice actor Alex Hirsch was even the guest-star of that episode.