William Afton (Five Nights at Freddy's)

"Follow me."

- The Killer

The Killer (or the Purple Guy/Man or The Murderer) is the true main antagonist in the Five Nights at Freddy's series. 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. He then 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 (it is also speculated that he wasn't really arrested and the one who was caught was simply a scapegoat). The prequel states that the killer was a purple man who is even possibly one of the security guards.

Role in the series
In the prequel, The Killer isn't mentioned up until Night 6 (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.

In the second game, 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 the player takes control 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 eventually be frozen in place forced to watch the children turn red. Freddy may have tried to stop him since the animatronics protect the kids, but once again failed. The game then ends with The Puppet's jumpscare. The dead child would later go on the possess the mentioned animatronic.

S.A.V.E T.H.E.M
In a minigame where Freddy is following The Puppet (while yelling 'Save Them" constantly), there is a very rare chance that near the end, the Killer will appear and kill Freddy while saying "You Can't", the game may terminate if this happens.

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 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 may have inadvertently helped the killer. The minigame then ends with Foxy's jumpscare.

Five Nights at Freddy's 3
The Killer appears in Five Nights at Freddy's 3 as the true main antagonist, inhabiting Springtrap in the present day. He appears in the minigames that act as cutscenes between each night. Instead of murdering children, however, he lures the animatronics one-by-one with a purple Freddy suit (possibly Shadow Freddy), and then ambushes them and dismantles them. In the "bad ending", you play as the ghost of what seems to be the Puppet or one of the original five animatronics, and chase the terrified Killer around. Eventually, the killer is cornered by the ghosts of the five murdered children. Attempting to flee, the Killer hides inside of Springtrap in order to protect himself. However, due to his breath, the suit's springlocks suddenly loosen up, and the suit closes in on him like an iron maiden (presumably caused by the suit's spring trap, hence the name of the character), crushing the Killer to death and ending his physical reign of terror, but also allowing him to possess the animatronic.

In the ending of the game, "Fazbear's Fright" burns down, presumably destroying both the animatronics and the remains of the Killer's body, killing him once and for all (although the brightened image of the newspaper image at the end shows that Springtrap could possibly still be alive).

In the minigame "Happiest Day" shows the spirits of the the children leave the animatronics, meaning the Killer's death finally set them free into the afterlife.

Personality
Not much is know about his true personality, but he seemed as to enjoy killing children as he smiles as he murders them. He may be traumatized with fear or guilt following the murders, causing him to return to the Pizzeria and destroy the animatronics (although this could have been an attempt to hide any evidence.)

Theories
Prior to the revelations of his fate at hands of the animatronics in the third game, there are several theories based upon clues that can be found in the prequels, which are:
 * In recent theories, several fans of this game have theorized that the Killer is really the security guard that the player plays as ;Mike Schmidt and later Jeremy Fitzgerald. Several hints throughout the game also indicate that this is all in the Killer's mind:
 * In the game, if the player manages to beat all five days, they 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. Also the check player gets upon beating Night 5 is dated for November 1987.
 * 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.
 * 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 very much like Schmidt himself.
 * 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.
 * There could be two killers, due to the fact that there are two different sprites of him (pink and purple).
 * There's a possibility that the Phone Guy is the perpetrator due to the fact that The Killer had a phone on his hand and a security guard badge on him. Though after the third game, this may not be true.
 * A theory is that Golden Freddy, instead of possibly being the 5th child murdered, is really the Killer reborn as an immensely powerful entity with powers even the Puppet does not possess. Golden Freddy itself also implied to be the very animatronic that the Killer once modified into actual costume before committing his killing spree.

Trivia

 * The Killer seems to like Foxy as he smiles at him as he exits Pirate's Cove in one of the Death Minigames. If this is why The Killer was smiling, it further suggests the theory that he is Phone Guy, as of this line, "Did Foxy ever appear in the hallway? Probably not. Like I said, he was always my favourite."
 * If the minigames are based on true events within the game (the crying child and the children in the Pirate Cove minigame), The Killer has murdered 10 to 11 (the same number of animatronics) children.
 * The Killer's motivation for killing the children is still a mystery, although many people assume he did simply for fun.
 * Before his actual fate revealed, people assume that the Phone Guy is the Killer due to him holding what appears to be a phone and wearing a badge in the minigames much like Phone Guy does.
 * He is somewhat similar to Freddy Krueger.
 * Both are child killers who enjoy what they're doing (the Murderer is always seen with a smile on his face).
 * In death, they became even more powerful than they were in life.
 * The Killer is similar to HABIT.
 * Both are shown to be the hidden driving force behind the story.
 * Both of their symbolic colors are purple.
 * Both murder children.
 * Both are described as a "smiling man".
 * HABIT's favorite food is pizza, the Killer's massacre takes place in a pizzeria.
 * Both are highly enigmatic villains.
 * Neither of them seem to have any motivation for the atrocities they commit other than for the fun of it.
 * Both are associated with rabbits.The Killer became Springtrap after his death.
 * The Killer is noticeably the only Five Night's at Freddy's character to be truly evil and malevolent.
 * The Killer ironically dies the same way he killed the children: being stuffed inside an animatronic suit.
 * His death was an accident due to one of the instructions from the Phone Guy was not to nudge the springlock or breathe on it as moisture would cause the springlock to break loose. The killer was laughing/breathing while in the suit, presumably causing moisture that resulted in the springlocks to loosen and crush him in the suit.