Bill Cipher

Bill Cipher is a dream/mind demon that can enter a person's subconscious. He can be summonded using an incantantion found on his page in Book 2: "Triangulum, entangulum. Veneforis dominus ventium. Veneforis venetisarium!", which, translated from it's original Latin, comes out to:  "Triangle — I invoke you. I come to the defensive barrier of the mind. I will see the barrier destroyed."

History
Bill, and the symbol he's based on: the Eye of Providence, appear frequently in Gravity Falls. He was the unseen author of the cryptograms in the online game Rumble's Revenge. His name and existence is deduced by taking all the capital letters in the cryptograms from Rumble's Revenge, to form the message: "MY NAME IS BILL."

A picture of Bill is shown briefly at the end of the opening theme. The picture is part of an image from his entry in 2|Book 2. Encircling him are various symbols that link to various characters in the show. Most notably, when he appears physically for the first time, he refers to Dipper, Mabel, and Soos, as "Pine Tree, Shooting star, and Question Mark" respectively. The entry also makes special note of the glasses symbol, the author of the book seemingly having been alarmed by this. Underneath "Name: ???" is the text: "This odd, triangular being has appeared in my dreams every night for weeks."

In his entry in 3|Book 3, we learn Bill's full name: Bill Cipher. Behind his name is a message encrypted with a symbol substitution cipher; when de-coded it reads: "Liar Monster. Snappy Dresser." There are various notes scattered about the page, such as "Is he watching me?" and "Bill has proven himself to be one of the friendliest and most trustworthy individuals that I've ever encountered in my life. What a guy! I honestly can't trust him more. Not evil in any way, Bill is a true gentleman." However, the latter note is crossed out and below another note reading "Can't Be..." can be found written in red ink. On the next page, a diagram of a human head and various aspects of the its mind is shown, it's top being opened up for a drawing of Bill to enter it. In the lower left corner of the page "DO NOT SUMMON AT ALL COSTS!" is written in large, red letters. The rest of the page is spattered with a dark red substance, possibly blood.

"Dreamscaperers" is the first time Bill is directly addressed and introduced in the series. Gideon Gleeful, in an attempt to take over the Mystery Shack once again, summons him. Gideon tells him to steal Stan's safe combination directly from his head, so that Gideon can steal the Shack's deed. Bill agrees once he knows it's Stan, but in return Gideon would have to help him in his own plans. Gideon agrees immediately and the two shake on it. Unbeknownst to Gideon, Mabel, and Soos witnessed the deal in the forest, and get Dipper's help to follow him into Stan's mind.

Once inside Stan's head, Bill confronts the trio and brags that he knows what they're all thinking. To prove his statement, he summons Xyler and Craz from Mabel's imagination. He tricks Mabel and Soos into looking for the memory of Stan's safe combination first, knowing they'd lead him straight to it. At some point Soos is separated from everyone else, and Bill takes his place. Once they find the correct memory he takes it and nearly escapes with it. But while he was reading out the combination to Gideon (who he was connected to), Mabel shoots the memory into another memory of the bottomless pit with a nyarf gun. Gideon breaks off their deal, to Bill's fury. Bill turns his anger towards Mabel and Soos by bringing their nightmares to life, and killing Xyler and Craz.

Dipper returns in a timely manner and tells Mabel and Soos that while they are in Stan's mindscape they can do whatever they want. They battle Bill and he is nearly defeated. And just as though it seems he will be forced out of Stan's head, he puts a stop to everything instead. Impressed, he decides to let them go, and after warning them of a mysterious darkness that will change everything they care about, he tells them that he'll be watching them. He leaves in a wheel almost identical to the one that appears in his entry in Book 2.

Personality
Bill is a fast-talking and physically irreverent demon who finds most things amusing (although no one is really sure why). He's outrageous and outlandish. Though he may come across as simply annoying, he's not to be taken lightly; when angered, he's a force to be reckoned with.



Appearance
Bill is a yellow, triangular creature that bears a strong resemblence to an Egyptian Pyramid. He has a single large eye rimmed with four short lashes on its top and bottom. He moves around largely by floating about, and rarely actually stands on his own two feet. He has thin, black limbs, wears a small, black bowtie, and has a tall, thin, black top hat that he "wears" which floats just above his head. He has also been seen carrying a small, black, cane.

Cameos
The following are sightings of Bill and the Eye of Providence, before his physical appearance in "Dreamscaperers" :

Trivia

 * He is based off of the Eye of Providence, which is most commonly seen on the back of the US$1 bill.
 * On the page about Bill in book 2, the -$12 bill says "Semper vigilantum," which in Latin means "always watching."
 * It is unknown what he wanted in return from Gideon when he got the safe code from Stan's memory.
 * Both Gideon and Dipper's journals contain sections on Bill, but curiously, Gideon's journal contains instructions on how to summon Bill, whereas Dipper's contains instructions on how to stop Bill if he is summoned.
 * The repition of the phrase "always watching", frequent appearences of his likeness, and his references to "buy gold" and other common conspiracy theory bylines are a reference to the Illuminati, a boogieman commonly believed by conspiracy theorists to use the Eye of Providence as it's symbol.
 * Bill was designed using Phi proportions, a number that approximates to 1.618.
 * In the Game Rumble's Revenge one of the codes is " I will be returning to Gravity Falls" indicating he knew that Gideon would summon him. How he knew this is unknown.