"Unspeakable Evil" is a common theme in topics dealing with villains or malevolent entities / people from theology and/or folklore - it refers to a phenomena found across multiple cultures in which the mere mention of the evil-doers' name is taboo and believed to bring bad luck to those who utter it or (in extreme causes) cause death, disease or other supernatural curses. "Unspeakable Evil" can also apply to individuals/beings who have gained such a level of infamy that the mention of their name, while by no means causing harm, is shunned upon - society as a whole (whether real or fiction) prefering to try and forget the evil-doer ever existed.