31. The killer is Mrs. Voorhees.
Movie: Friday the 13th (1980)
Writer: Victor Miller
As Scream's clever opening sequence proved, one of the best ways for a horror buff to test someone's genre knowledge is to ask the following question: Who's the killer in the original Friday the 13th? Chances are, those who've never heard of Rue Morgue magazine or fantasized about Linnea Quigley will answer with, “Jason Voorhees,” but, alas, they'd be dead wrong.
The impossible-to-kill Jason didn't make his debut until 1981's Friday the 13th: Part II; in the 1980 franchise-starter, screenwriter Victor Miller opted for a more surprising slasher in the form of Mrs. Voorhees (Betsy Palmer), the mother of Jason, a disabled kid who drowned at Camp Crystal Lake 22 years prior, no thanks to the careless counselors. See, now you're one of us cool, trivia-ready horror fans.