William Afton (Five Nights at Freddy's)

"you can't"

- The Killer

"Follow me."

- The Killer, luring the animatronics to the safe room.

The Killer (or the Purple Guy/Man or The Murderer, in the alternate universe novel Five Nights at Freddy's: The Silver Eyes called William Afton/Dave Miller) is the main antagonist of the Five Nights at Freddy's series.

The Killer was a man who dressed up as one of the mascots at Freddy Fazbear's Pizza (theorized to be Golden Freddy or Springtrap) and used his kid-friendly disguise to lure five children into the back of the pizzeria. He then murdered them and left their bodies behind, only for them to be stuffed into the mascots' costumes (Freddy, Chica, Bonnie, Foxy, and Golden freddy ) by the Puppet. Someone was arrested the following day and charged, but his current status and influence on the game's events are unknown, while the killer was still free. The prequel states that the killer was a purple man (not a costume or suit) who is possibly one of the security guards.

Role in the franchise
A man who no one has ever seen or heard of emerged in Freddy Fazbear's Pizza with plans of death and chaos for the company simply for the sake of it. A man with no name or motives, a villain driven by a lust to create social disorder and desired nothing but anarchy to feed his sadistic appetites and morbid, dark sense of humor.

One day, in Fredbear's Family Diner, as Freddy Fazbear was serving cake to the children, a child was crying outside for an unknown reason. As he cried, a man drove over in a purple car and murdered the child. Freddy could not protect the child, for if he was to venture outside the pizzeria he would be deactivated. With that, the man drove away leaving the child's corpse outside. The child, driven by revenge, possessed an animatronic a certain time after that, known as the Puppet.

Years later Fredbear's Family Diner is sold out and Freddy Fazbear's Pizzeria opens only for the man to return. This time the man killed five children outside Pirate Cove, pinning the blame on the animatronic inside, causing it to be shut down.

Years later, the man returned to the pizzeria and found a yellow suit and lured six children to a quiet part of the building and murdered them.

Five Nights at Freddy's 3
The Killer appears in Five Nights at Freddy's 3 as the main antagonist of the game, inhabiting Springtrap in the present day. He appears in the mini-games that act as cutscenes between each night. Instead of murdering children like in the previous game, instead, ambushes the suits they were stuffed in, and dismantles them. In the "Bad Ending", you play as the crying child who seems to be the ghost of the Puppet or one of the original five animatronics. After floating around the pizzeria, the player will eventually find a room filled with the other dead children and the Murderer himself, who seems to be panicking. When the player approach the Murderer, he will run away from them. 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. He stands up and laughs at his victims, thinking he has won, but due to the rain dripping from the ceiling the suit closes in on him like an iron maiden (presumably caused by the suit's spring trap, hence the name of the character), gutting the Killer to death and ending his physical reign of terror, but also possibly allowing him to possess the animatronic as a zombie, due to the teaser images of Springtrap showing the Purple Guy's corpse inside.

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 mini-game "Happiest Day", it shows the spirits of the the children leaving the animatronics, meaning the Killer's death finally set them free into the afterlife. Although, one head in the image was missing, possibly hinting at a later sequel.

Five Nights at Freddy's 4
The Killer can be seen in the mini-game of Night 4, presumably helping one of the employees put on the Spring-Bonnie suit.

Five Nights at Freddy's: The Silver Eyes
See here

Personality
The Killer is the confirmed murderer of the children that sparked the downfall of Freddy Fazbear's Pizza and started the chain of events that leads players through the series.

Judging by his actions and appearance within the mini-games, the Killer is cruel, ruthless and cold-blooded, taking sadistic pleasure in his crimes with a smile. It isn't until he is confronted by the ghosts of the five kids that he shows any other emotion - panic and concern for his own life. His motives are unknown, but deliberate.

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 favorite."
 * However, he also smiles when he chases Freddy in the SAVETHEM mini game and when he dismantles the animatronics in the third game.
 * 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 children.
 * The Killer's motivation for killing the children is still a mystery, although many people assume he did simply for his own enjoyment. The reason he kept returning to the same location is unknown, however.
 * 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. The reason the Killer was holding a phone
 * The Five nights at Freddy's 2 phone calls heavily imply that the Dayshift security gaurd was the killer due to the dayshift gaurd not having reported the murders being a suspect for the police causing the place to go on lockdown and being an employee at the restaurant as well as him being the only one who could be there during the SAVETHEM minigame.
 * He is somewhat similar to Freddy Krueger.
 * Both are child killers who enjoy what they're doing (the Murderer is almost always seen with a smile on his face).
 * In death, they became even more powerful than they were in life.
 * The Killer is noticeably the only Five Night's at Freddy's villain 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 move too quick, to not let the moisture touch the springlock which would cause the springlock to snap. The killer stood up quickly, was laughing/breathing while in the suit, and wore it during it was raining as the roof was leaking presumably causing moisture that resulted in the springlocks to snap and crush him in the suit.
 * As Big Brother later revealed to be the true culprit of The Bite of '87 and some implied that he was the witness of the incident, The Killer's actual motivation in killing the children and stuffed the children into Freddy, Chica, Bonnie, Foxy and Golden Freddy was to avenge Big Brother's killed sibling albeit he also gone too far. But this was yet to be confirmed.
 * In the novel Five Nights at Freddy's: The Silver Eyes, The Killer's full name was revealed as William Afton, which he later changed to Dave Miller. However, this novel is confirmed to be a different universe.
 * Yellowjacket aka. Darren Cross also has a similar death. He also has  insanely  death screams and was crushed by his suit