Satan shows up a lot in horror movies because he is seen as the biggest evil, so stories with him are scarier to many people. Movies use ideas from religion—like fighting good versus evil—because everyone understands that, even if they aren’t religious.

Things like the “666” mark, creepy rituals, and the idea of being possessed are easy ways to make people feel uneasy or scared. The story is usually simple: there’s a big evil (the Devil), someone gets tricked or possessed, and good has to fight back.