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).
Purple Guy got into the Spring Trap thinking he would be safe only to be crushed and bleeding out to his death. However according to the voice messages of the purple guy (the one on cassets types that had been found) there was an unfortuante accident happen.