When William Afton died in a Spring Bonnie (Yellow Rabbit) suit, a monster was born. Springtrap. At least, that is how he starts out until he finds out Sky's true identity. Afton, unlike the normal story. Was running from the insane, crazed Funtime Freddy model (not the one everyone meets at the start) that was chasing him. Afton frantically put on his Yellow Rabbit costume, but due to being so frantic and not careful, the springlocks snapped.

He has three personalities. 

1) His Own, William Afton. William is the murderer of all the kids and adults that ended up possessing animatronics. Every time he took someone's life, it took a bit of his sanity. He thought he was doing all this to save his children. But he was wrong, he did it because he enjoyed it.

2) His Loud Self, Springtrap. This is what he becomes when he finally accepts the monster he is. Even if he has guilt, he doesn't show it. Infact he makes jokes on everything, even Henry's line of "the darkest pit of hell has opened to swallow you hole". He is almost like what a theatre kid was back in the day, but its now Springtrap.3) His Persona, Spring Bonnie. Sometimes the suit plays its automated voice lines back from when it had an animatronic mode at Fredbear's Family Diner. The malfunction of the suit causes it. It drives Afton insane whenever it does, but he deals with it anyway. Since it can't be deactivated.