William Afton (Five Nights at Freddy's)

Wlliam Afton (or the Purple Guy/Man or The Murderer) is the main antagonist of the entire Five Nights at Freddy's series. William Afton was a man who dressed up as one of the mascots at Freddy Fazbear's Pizza (most likely Spring Bonnie or perhaps Golden Freddy) 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.

Role in the franchise
An unknown man emerged in Freddy Fazbear's Pizza with plans of death and chaos for the company. A sinister inventor driven by a lust to create life from death and experiment on children 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, the man drove over in a purple car and murdered the child. Freddy could not protect the child. With that, the man 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 sold out and Freddy Fazbear's Pizza opens only for the man to return. This time, the man killed five children outside Pirate Cove.

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

On the third playthrough, Afton, 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.

Five Nights at Freddy's: Sister Location
In the opening scene of Sister Location, an entrepreneur is asking William Afton questions about the new animatronics. They inquire why certain features were added and express their concerns, but he avoids answering the specific features they refer to.

He is also the creator of the animatronics and the former owner of the Circus Baby's Entertainment and Rental and, by extension, Circus Baby's Pizza World.

Personality
William Afton 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 minigames, William Afton is cruel, ruthless and cold-blooded, 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 Freddy Fazbear's Pizza for personal issues, simply kill for enjoyment, or enact a gambit to intentionally trap the spirits of his victims inside the animatronics.

Trivia

 * William Afton 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), Afton has murdered at least 11 children.
 * His actual motivation for killing the children is still a mystery, although many people assume he did for his own enjoyment. Sister Location brings up the possibility that William Afton's intentions were to harvest the children's souls, and create life within the animatronics. The reason he kept returning to the same location is unknown, however.
 * 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.
 * William Afton is noticeably the only Five Nights at Freddy's villain to be truly evil and malevolent.
 * Sister Location confirms that he is the creator of the Circus Baby's Pizza World animatronics, and that he invented them with abilities to abduct and kill children.
 * Before Sister Location was released, Michael Afton was thought to be the same entity as William Afton, but it was revealed in the final cutscene in V. Hard Golden Freddy mode (Custom Night) that he was not.
 * William seems to have a British accent, with his daughter and son having one too.
 * William seems to have 2 confirmed children; his son, Michael Afton, and an unnamed daughter (the girl who was killed by Circus Baby). However, it is not confirmed if the Crying Child and Older Brother from the fourth game are also part of the Afton family or not.