In some ancient civilizations the Wolf was a symbol of the underworld. In Egypt, the guardian of the dead was Anubis who was a wolf-headed god. The jackal portrayed as black was the symbol of both death and regeneration.
William is also the one who hid inside the suits and kidnapped and killed children, leading to the assumption that William Afton is The Purple Guy of FNaF 2 and 3 (he is killed at the end of the book when Charlie sets off the spring locks in his suit).
The main characters in the Five Nights at Freddy's series are generally security guards working at a Freddy Fazbear's Pizza or related location. None of them have distinct personalities and most of the gameplay takes place from their point of view. In Five Nights at Freddy's, the guard's name is Mike Schmidt.