William Afton, the most deranged character in the fnaf franchise, the one who ruined so many lives, yet has so many fans in the real world...

why is that?

For the aspect of why his character is the way he is, I'd honestly say from my perspective, he's just a narcassistic sociopath who doesn't want anything but power, and will do whatever it takes to get that. He thrives in the pain of others, and he manipulates his way to get what he wants. His drive for immortality and his desire for power makes him not insane, but simply a narcassistic sociopath.

He even goes as far as to see his children's deaths as stepping stones to his ultimate goal - power. He sees his children only as pawns in his game, as puppets.(no pun intended.)

Personally, I feel as if the 'tumblr sexyman' era of the internet had a huge impact on why the fnaf fanbase seems to love William so much. They find him attractive, which, for me is odd given his ONLY canon designs are the graphic novel design and the fnaf movies' portrayal. I feel as if the art community had a lot to do with the hype for him, which, again, to me is odd, because hes a serial killer (and a middle aged man.) His actions ultimately resulted in approximately 28 games, over 20 books, and a lot of tragedy. Scott Cawthon, the creator of the fnaf universe, has also indirectly stated that the main 5 missing children that Afton slaughtered aren't the only victims, and that there's more victims than we'll ever be aware of.

Afton's "death":

Springlocks.. the one fault in Afton's creations; the fault that ultimately led to his demise, but not his downfall.

Due to his deeds, William can't die, which is what he wanted, just not under the circumstances he ended up with. The animatronics have a mechanism that makes them wearable, separating the mechanics from the outer shell. In the fnaf universe, this is called springlocks. Springlocks allow the wearer to not be touched by the animatronic's machinery, but still allowing someone to wear the animatronic suit. The remnant, which is what he gained by killing children, when collected enough, can lead to immortality. He shoved the corpses of the victims into the animatronics, the springlocks ensuring they can't be seen from the outside. While to William, this might have been seen as smart, it was actually very stupid considering that the souls of the victims were then connected to the animatronic they were stuffed into.

The vengeful souls then hunted him, leading to him hiding in his Spring Bonnie suit, (aka the suit that he wore to lure them in originally.) He thought he was safe, but considering the springlocks, he wasn't. The springlocks crushed him, ensuring a slow and agonizingly painful "death" for Afton. 60 years he was left to rot in that suit, which, also happened to the victims, as no one ever thought to check the animatronics while investigating the missing children. Then, after 60 years, he came back, albiet, now quite literally being stuck in the animatronic suit, his corpse merged with it...