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 Purple Guy and His Appearance in The Silver Eyes. The Five Nights at Freddy's novel, The Silver Eyes, follows 17-year-old Charlotte Charlie as she revisits the old Freddy Fazbear's pizzeria her father owned along with her friends to pay tribute to their friend Michael who was killed at the pizzeria ten years ago.