William Afton (Five Nights at Freddy's)

The Killer is an unseen villain in the video game: Five Nights at Freddy's. He is only mentioned in apparent newspaper excerpts on posters in the game.

Role in the game
The killer was a man who dressed up as one of the mascots at Freddy Fazbear's Pizza and used his kid-friendly disguise to lure five children into the back of the pizzeria. It is assumed he murdered them and stuffed their remains into the mascots' costumes. He was arrested the following day and charged, but his current status and influence on the game's events is unknown.

Theories
Recently, several fans of this game have theorized that the Killer is really the security guard that the player plays as; Mike Schmidt. Several hints throughout the game also indicate that this is all in the Killer's mind:
 * In the game, if the player managed to beat all five days, the player will receive a check of $120.00, and since the player has to endure six hours (12:00am to 6:00pm) for five days, the player receives $4 an hour. This hints that this game takes place somewhere between 1980s and to 1995, but sometime after the The Bite of '87.
 * It's also been hinted that the Killer may've the one responsible for the Bite of '87 for tampering with the animatronic, which resulted in one of them biting the frontal lobe off a child. If the player endures the 7th night, the player receives a pink slip (or a termination slip), for tampering with the animatronics, general unprofessionalism and odor. So, for revenge, the Killer disguised himself as a mascot, lured five children and stuffed them in the animatronic, hoping that the place will be forced to close down.
 * Throughout the game, the player encounter several hallucinations. One of them is a split second of the words; "It's Me!".
 * When the player observes the other rooms via security cameras, one may encounter various messages appearing and disappearing, including the words; "It's Me".
 * Even though the reports never say that a former employee was the Killer, the killer must've had access and knowledge of the Employees Only Room.
 * While in the security room, the player can spot cobweb, indicating that Freddy Fazbear's Pizza is already closed down.