Billy is a puppet that has appeared in the Saw franchise. It was used by John Kramer to communicate with his test subjects by delivering recorded messages, often appearing on a television screen or occasionally in person to describe the details of the traps and the means by which the test subjects could survive.
In the film series, before becoming the Jigsaw Killer, John created Billy to be given as a toy to his unborn child. However, Jill, his wife, is shown to miscarry after being hit in the stomach by a swinging hospital door due to Cecil ramming it open without looking. John's unresolved anger was likely a primary motive for creating the puppet as a vehicle for his instructions to trap victims. The traps he created can be seen as a manifestation of his anger with people who he feels do not appreciate having their life, when his unborn baby was killed before having a life of its own.
Although never actually identified in the films, "Billy" is the name by which writers, directors, and members of the cast and crew refer to it in documentaries and interviews. The name was given to it by Australian creator James Wan, who is the director and co-writer of Saw. Some claim that the name is spelled "Billie", though Wan himself spells it "Billy".
The endurance and popularity of the Saw franchise has resulted in the production of Billy merchandise, as well as references in other media.
In the first Saw film, Billy is seen on a television set by Amanda Young, telling her about the reverse bear trap that was hooked into her jaws, and explaining that the key to remove it is in the stomach of her "dead cellmate" (who is actually a heavily sedated man) lying in the room. After she disembowels the man and frees herself, Billy comes into the room on his tricycle to congratulate her.
Later, Adam remembers seeing the puppet in his apartment when the lights went out. As he searches the dark rooms using his camera's flash, the puppet's eerie laugh rings through the apartment, and Adam hits it with a bat until it stops.
When Detectives David Tapp and Steven Sing discover Jigsaw's latest hideout, they remove blankets from several covered items, one of which is Billy.
In Saw II, Billy is seen on the screen at the beginning of the film, giving Michael hints about the death mask he is wearing.
Later, when the detectives discover Jigsaw's new hideout, several officers walk up a caged staircase and are greeted by Billy, who wheels into sight at the top of the stairs on his tricycle and laughs. The cage then becomes electrified after one officer steps on a rigged step that breaks his legs.
In a flashback in Saw III, Jigsaw is seen constructing Billy for Amanda's game, painting the puppet's face. Later, Billy appears on videotape to inform Troy and Kerry of their respective traps.
Billy is also used to remind Jeff Denlon of his dead son, by appearing next to his tricycle in the same position Jeff's son was in when he was killed. The puppet gives a mocking laugh until Jeff beats it into silence.
Billy is first seen in Saw IV when Officer Daniel Rigg awakes after being attacked in his apartment and rendered unconscious. Rigg opens his bathroom door, pulling a trigger wire from a TV set. Billy appears on the screen to explain Rigg's game. Upon leaving the room, Rigg is greeted by another message concerning his first test, referring to a woman Jigsaw deemed to be a criminal, who had been placed in a machine that would scalp her.
Agents Peter Strahm and Lindsey Perez later find Billy in a room in a school, sitting on a chair surrounded by candles. From a microcassette recorder hung around the puppet's neck, Perez learns that her partner will soon take the life of an innocent man (later revealed to be Jeff Denlon), and that her next move is critical. Billy's eyes begin turning to Perez. She leans in to hear this last, at which point Billy's face explodes, blowing shrapnel into her face and neck. Perez collapses into Strahm's arms as Billy laughs.
There is also a flashback of Jigsaw giving a less menacing, early version of Billy to Jill Tuck as a gift for their unborn son Gideon. An interview with Tobin Bell revealed that this was the beginning of a storyline concerning Billy's origins, as that of his tricycle, to be explored in future Saw films.
Billy appears in the opening sequence to tell Seth Baxter the rules of his game. It is unknown how Hoffman created the videotape for this game. According to a list of potential Jigsaw victims, Seth was the third person tested after Cecil and Mark. In those tests, Jigsaw did not use a puppet. However, Jigsaw's testing spree had already begun beforehand, as shown during the events of Jigsaw, where Billy does appear.
Billy is also seen at the beginning of the tests designed for Ashley, Luba Gibbs, Charles, Brit, and Mallick.
In Saw VI, Billy appears on tape in the opening trap, which pits Simone and Eddie against each other. He also addresses William Easton during two of his four tests. He appears in William's second test hanging from a noose, and on videotape in the fourth test. Saw VI marks the first time Billy appears "in person" to deliver test details to victims.
Billy appears in Saw 3D. He gives Brad and Ryan instructions for their trap in person, does the same for Bobby Dagen's second test, and appears on videotape for the others. When Hoffman goes to his hideout after he escapes the Reverse Beartrap, multiple Billy heads can be seen. Billy's final appearance is in Hoffman's secret hideout at the end of the film; Hoffman blows it up, destroying Billy in the explosion.
Billy appears in Jigsaw. This time, he has illuminated eyes and shoes. He appears on his tricycle with a letter around his neck with the word "Confess" written on it. He later appears on a videotape with his eyes illuminated, explaining to Ryan how he can save Anna and Mitch before they are buried alive.
A photograph of Billy is seen in Spiral, while the film's Jigsaw copycat killer and main antagonist, Billy Emmerson (portrayed by Max Minghella as an adult and Leonidas Castrounis as a child) is named in tribute to the puppet. Masquerading as police detective "William Schenk", Emmerson showcases his own new puppet inspired by both Billy and the pig motif of the previous films.