William Afton (Five Nights at Freddy's)

Purple Guy(or The Murderer) is the main antagonist of the entire Five Nights at Freddy's series. Purple Guy was a man who dressed up as one of the mascots at Freddy Fazbear's Pizza (most likely Golden Freddy or Springtrap) and used his kid-friendly disguise to lure five children into the Safe Room, where there were no security cameras.

He then murdered them and left their bodies behind, only for them to have possibly be stuffed into the mascots' costumes (Freddy, Chica, Bonnie, Foxy, and Golden Freddy) by the Puppet. Someone was arrested eventually and charged, but his current status and influence on the game's events are unknown, while the real killer was still free.

The prequel depicts the killer as a pink man (not a costume or suit) in the minigames, who is possibly one of the security guards. Enough evidence could support him being a security guard or a technician.

Role in the franchise
An unknown man emerged in Freddy Fazbear's Pizza with plans of death and chaos for the company.

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, Purple Guy drove over in a purple car and murdered the child.

Freddy was unable to protect the child. With that, Purple Guy drove away, leaving the child's corpse outside. The child, possibly driven by revenge, was theorized to have possessed an animatronic a certain time after that, known as the Puppet.

Years later, Fredbear's Family Diner is shut down. An incident occurred, an event where a boy was bitten in the head by Fredbear, inflicting severe damage to the frontal lobe of his brain, when the restaurant made a resurgence, only for the establishment to close down again. Later, Fazbear Entertainment, in presumably 1973, opens Freddy Fazbear's Pizza, only for Purple Guy to return. This time, Purple Guy killed five children outside Pirate Cove.

Five Nights at Freddy's 2
In Five Nights at Freddy's 2, Purple Guy can be seen in the Foxy Go! Go! Go! Minigame.

On the third playthrough, Purple Guy, who killed the crying child in the Take Cake to the Children minigame, is seen standing in the corner of the starting room, smiling. When Foxy approaches the children, they seem lifeless. The minigame ends with Foxy's jumpscare.

He also appears in the S-A-V-E-T-H-E-M minigame on rare occasions, where he attacks Freddy and crashs the game, by saying "You can't" which is responding to the various messages about saving the children.

Five Nights at Freddy's: Sister Location
Purple Guy may be "Eggs Benedict" (as nicknamed by the HandUnit), the main protagonist of Five Nights at Freddy's: Sister Location.

He is only seen in the cutscenes, where his body is getting rotten more and more, until have a similar appearance to the previous games; a tall, purplish man with glowing eyes.

Personality
Purple Guy is the confirmed murderer of the children that sparked the downfall of Fredbear's Family Diner and the two Freddy Fazbear's Pizza establishments, orchestrating the chain of events that leads players through the series.

Judging by his actions and appearance within the minigames, Purple Guy is cruel, ruthless, aggressive, temperamental, cold-blooded, and manipulative to even his own son, taking sadistic pleasure in his crimes with a smile. His motives are unknown, whether it is to cause chaos, take revenge of the owners of Fredbear's Family Diner and Freddy Fazbear's Pizza for personal issues, simply kill for enjoyment.

Trivia

 * Purple Guy seems to like Foxy as he smiles at him as he exits Pirate's Cove in one of the Death Minigames.
 * If the minigames are based on true events within the game (the crying child and the children in the Pirate Cove minigame), Purple Guy has murdered at least eleven children.
 * His actual motivation for killing the children is still a mystery, although many people assume he did for his own enjoyment.
 * Before his voice was revealed, people assumed that the Phone Guy was Purple Guy, due to him holding what appears to be a phone and wearing a badge in the minigames, much like Phone Guy does.
 * The Five Nights at Freddy's 2 phone calls heavily imply that the dayshift security guard was the killer, due to the dayshift guard 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.
 * Sister Location implies that he is the son of William Afton.
 * Purple Guy seems to have a British accent, with his father and sister having one too.
 * Purple Guy is rumored to be the Older Brother from the fourth game, while it's probably not the case.
 * Purple Guy is shown to be a very tall man. In his appearance in the fourth game, he towers over other adults. In the third game, he is taller than the animatronics.