Before getting into the theory itself, let me put the basis: At this point is clear that there must be at least 2 purple man. One William, the other Michael. However I firmly believe that there’s a third unnamed one, and that this one is also a killer.
I’ve been asked before why this third one exist, what purpose it serves having another killer. The explanation is actually simple, it’s a retcon (the retcon), and it was introduced as early as FNAF 2. In fact, with the introduction of the second instalment of the series many things were expanded or changed from what, I suspect, was the original plan.
The original idea, meant to be only inside FNAF 1, was to have a killer murder 5 kids, one of them being the protagonist’s sister. I’m saying it’s her because of Sister Location, otherwise it would have been left unknown the reason for why Mike came to work at Freddy’s. She would be the reason for the original meaning of the ‘It’s me’ phrase, but I perhaps this was also changed during FNAF 2.
Returning to the point of the villain of FNAF, Scott already implied during FNAF 1 in the newspaper clips that it was a worker the one who committed the murders and that would be the end of it if FNAF didn’t became famous.
But FNAF became famous, and Scott had to expand the story.
Scott thought of a better villain, this one would be the company’s CEO, in other words, William. But he couldn’t write off the newspaper clip murderer, the worker of Freddy’s, so he had to include it; indirectly creating an even bigger mystery in the process.
That’s why there are two sets of murders with 5 dead kids each. William had to fit the “murderer quota” and had more victims than just the puppet (imagine if William had just killed the puppet). That way, the newspaper clips murder became the one seen in the SAVETHEM mingame (done by a Freddy’s employee), and GOGOGO! shows the one made by William and they’ll become the original 5.
The newspaper clips was retconed from showing us the origin story of the animatronics, to showing us another murder entirely. This second set gave way to the possession of the Toy animatronics.
I think that the surname Afton came actually after FNAF 2, the reason why Mike and Fritz have so similar surnames was because they were meant to be brothers from the beginning, but Scott hadn’t set for a proper surname yet. So Schmidt/Smith was meant to the working surname.
Another thing that could have been changed was the sister. Now she is in Baby, but I suspect the original idea was to have her possess Golden Freddy, hence the girl’s laugh. But there’s a twist for this, the reason for Freddy to get in the girl’s bathroom was because, Michael had to suspect him to be his sister. Freddy’s laugh is a slowed down girl’s laugh, and it was meant to be (from an in-universe perspective) a red herring. Michael was meant from the very begging to be searching for his sister, and only in Sister Location he fulfils his mission.
The ‘It’s me’ phrase was meant to be referring to the sister, her being Golden Freddy, however, the meaning changed, and now it’s simply attributed to Golden Freddy. I still haven’t given it a proper explanation for its meaning as of now; I simply know that the original meaning changed.
There’s a difference between what I suspect were the original plans (Golden Freddy being the sister), and what we now have. Currently, Golden Freddy isn’t anyone related to the Aftons. Golden Freddy is not the sister, and much less the Crying Child. Remember that Golden Freddy is part of the original 5 murder and that they were already dead when the Crying Child is alive, so he cannot be Golden Freddy.
If my guess is right and the dreams in FNAF 2 belongs to the elder brother (Fritz Afton AKA Fritz Smith), then it might mean that Golden Freddy is looking for him, and that Michael during FNAF 1 has been somehow been confused with a family member again (his elder brother Fritz). Or alternatively, Golden Freddy during FNAF 2 was still meaning to be the sister and she would be trying to get in contact with her siblings. Obviously, Sister Location changed plans completely.
A minor detail that I want to point is the 1987 easter egg with Golden Freddy. When was it included, before or after FNAF 2 was planned/teased? The answer is after it was teased, and I have an idea to why it is. I think that originally it was meant to be Foxy the one who did the bite (being out of order, having a broken jaw..), but with the FNAF expansion from 1 to 2, Scott changed it to Fredbear (shown then by Golden Freddy). The reason behind this would be being more dramatic, the animatronic possessed by the sister would be the one that almost kills her brother accidentally, however, as we’ve seen the idea was partially discarded.
There’s a funny observation. The sister being Golden Freddy was given a nod during FNAF 4, with her possessing the Fredbear Plush.
This retcon feels like in the original trilogy of Star Wars, when Obi Wan said during episode IV that Vader killed Anakin (they were meant to be different persons) and in the Empire Strikes Back, Vader reveals that he’s Luke’s father (that he’s Anakin).
So in short:
The retcon is the murder told in the newspaper: The original idea was that a Freddy’s employee murdered 5 kids, among them the sister of Mike, who would become Golden Freddy and the rest would become Freddy, Bonnie, Chica and Foxy. Now: The murder told in the newspaper is not the origin story of the animatronics, instead, it told us how a second set of murders went, giving place to the possession of the Toy animatronics; the murderer of the Original 5 is not an employee but the CEO of Freddy’s William Afton; and finally the sister wasn’t killed by a man but by Baby and ended hunting her instead of Golden Freddy. The murder counts as the retcon because it isn’t the origin story anymore, the sister’s fate is not because it wasn’t told directly in the first place and it didn’t have to be changed from what we were told.