William Afton (Five Nights at Freddy's)

"It's been so long. Since I last have seen my son lost to this monster to the man behind the slaughter."

- Lyrics that describe the killer in the song It's Been So Long.

The Killer is an unseen villain in the video game: Five Nights at Freddy's and Five Nights at Freddy's 2. He is only mentioned in apparent newspaper excerpts on posters 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. The prequel states that the killer was a purple man who possible can be somehow associated with Puppet (if Puppet has anything to do with murders) or even can be one of security guards.

Role in the series
In the prequel, The Killer isn't mentioned up until the 6th night (that presumably takes place after the murders), Phone Guy states the place is closed down because someone (heavily implied to be the killer) stole a spare yellow suit, and none of the Animatronics are behaving right.

The Killer also appears in the very cryptic "Death Mini-Games" which are sometimes triggered when the player dies. Failing and even winning the game will result in a jumpscare (except for one).

Take Cake to the Children
He first appears in the "Take Cake To the Children" game where have to please a bunch of children by giving them cake, all while playing as Freddy.

As the player tries to serve cake to all six kids, a purple car will pull up outside and a purple person gets out, then proceeds to kill the sad child (who actually appears to stop crying and then cry even harder while this is happening).

The sad child will then turn gray when dead. All the while, letters are called out, spelling "S-A-V-E-H-I-M", and the player begins to move slower and slower. If the player is able to make all the children green at the same time, the player will be unable to move and will be forced to watch the children turn red. Freddy may have tried to stop him since the animatronics protect the kids, but once again failed. Failing the game will result in a Golden Freddy jumpscare, winning will result in a Chica jumpscare.

Foxy Minigame
Playing as Foxy, the player walks out of what appears to be the curtained Pirates Cove and into a room with children, who celebrate his arrival. All five children appear to be happy, with the bottom one offset so it looks sad due to the black bars. The player is then returned to the curtained area and has to repeat this twice.

On the third playthrough, the purple man who killed the crying child in the Take Cake to the Children minigame (see above) is seen standing in the corner of the starting room, smiling mockingly at Foxy. When Foxy approaches the children, they seem lifeless. It is possible that the cake was poisoned by the killer and Foxy did not know it. (also further suggesting that the killer worked for the restaurant.) Therefore, Foxy inadvertently helped the killer. The minigame then ends with Foxy's jumpscare.

Personality
Not much is know about his personality, but he seemed to enjoy killing and murdering the children as he always smiles.

Theories
1. 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: 2. The killer is also rumored to be The Puppet.
 * 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 6:00am) for five days, the player receives $4 an hour. This hints that this game takes place somewhere between late 1980s and to 1995, but sometime after the The Bite of '87.
 * It's also been hinted that the Killer may've been 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!".
 * Phone Guy due to the fact that the killer had a phone on his hand and a secruty guard badge on him.
 * When the player observes the other rooms via security cameras, one may encounter various messages appearing and disappearing, including the words; "It's Me" again.
 * 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 and right window of security room is seemingly broken if turn on the light for Chica to be there, indicating that Freddy Fazbear's Pizza is already closed down.