William Afton is a child murdering scumbag, who only seemed to care for his family. But why did William commit all the atrocities that he did? In my eyes William has 2 personas; one beingAfton the buisnessman and father, while the other is the "Purple Guy", the dark side of his personality, the suited serial killer. I do not believe he hungered after Remnant, at least not intially. During the MCI, he was a "typical" child murderer, killing them for his own enjoyment, as would do again in 1987, posing as a security guard, taking the Dayshift and striking again, although perhaps this was to put Fazbear Entertainment out of buisness. He would see the animatronics haunted, he discovered Remnant, and became even worse; designing animatronics to capture and kill children, and injecting his robots with Remnant. Perhaps, like his book counterpart, he wanted immortality, perhaps he just wanted to see children die both physically, and spritually, wanting them to lose themselves in the animatronic as seen in Baby and Molten Freddy.
In terms of his children I believe he genuinely loved Elizabeth most of all, not wanting her to get killed. As for Michael, if The Immortal and the Restless is symbolic of Michael's childhood, William was not initially caring of Michael, but later became more loving, in his own way. If Micheal is the Older Brother, then William's love of him presumably lessened, with William being willing to send Micheal on a suicide mission. However William could never bring himself to kill Michael, as a human anyway. As for the CC, I think William was rather neglectful to him, due to barely acknowledging his existence.
Eventually Afton was killed after dissapearing to dismantle the Classics, presumably to cover up his sins, but ironically, he showed just how much he did not understand, as the ghosts did not need a body to threaten him. Terrified of paranormal retribution, William ran to the old Spring Bonnie suit, to scare the souls away by wearing the suit he lured them away and killed them in. When they stopped following him, he thought it worked, even laughing at their seeming cowardice. Hoever they were just waiting for the suit to malfunction, which it did, trapping William in the suit as some karmic justice. William was trapped in the Safe Room due to the Paradox of the suit existing to a room it could not detect, meaning William was trapped in the room for the better part of 30 years. His death, coupled with this long imprisonment, destroyed what was left of William's humanity, turning him into Springtrap, the Purple Guy persona, completly. The Children had delayed William, not defeated him, as now he had the potential to be the greatest serial killer of all time. He was freed by the Fazbear Fright Crew, and began to hunt the Guard stationed there, even if the suit could be distracted by the sound system. Even the fire could not stop him as he escaped, changed suit, perhaps to function 24 hours and went to the the Simulated Pizzeria. There he saw Mike, and this time nothing was going to stop him from killing Michael if he had to. In the end though, Afton's muderous intent was foiled by two things, the suit still being attracted to sounds, delaying him for days, and his former friend Henry springing the fire, destroying him forever, and sending him down to Hell, perhaps a specially designed one... by the one he should not have killed.