William Afton (Five Nights at Freddy's)

William Afton (or the Pink Guy/Man or The Murderer) is the true 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 (theorized to be Spring Bonnie aka 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 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 states that the killer was a pink 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 known as William Afton 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 apparent 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, Afton 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 causing it to be shut down.

Five Nights at Freddy's 4
In Five Nights at Freddy's 4, the Purple Man (either William or his son Michael) can be seen in the mini-game of Night 4, presumably helping one of the employees put on the Spring-Bonnie suit then suddenly the door closes after helping him put it on.

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

Five Nights at Freddy's: Sister Location
Afton is heard speaking for a brief moment during the start of the game, talking to another individual about Circus Baby. He lists everything she can do, though the other man seem uninterested in any of them.

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 mini-games, 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, or he is simply killing for sport.

In Sister Location, he speaks in a business like demeanor and he did love his daughter enough to avoid his own creations.

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 10 to 11 children.
 * His motivation for killing the children is still a mystery, although many people assume he did it for revenge. The reason he kept returning to the same location is unknown, however.
 * Before his voice was revealed, people assumed that the Phone Guy was the 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 Day shift security guard was the killer due to the day shift 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.
 * It was believed for a whole year that William Afton was actually Springtrap (Five Nights at Freddy's), but it was later reaveled that it was actually his son, Michael Afton, who was the same person who  Ennard scooped. This could mean that he's still alive.
 * Afton is noticeably the only Five Night's at Freddy's villain to be truly evil and malevolent, although even he has a sympathetic side, as he truly loves his daughter and regrets what happened to her.
 * It was also confirmed that he is the creator of the Funtime animatronics.