There's been plenty of debate over whether or not Alfred Hitchcock's masterpiece Psycho is a slasher movie or not, but I'm firmly in the camp that says it is. OK, so Norman Bates doesn't roam around looking for his victims — they unwittingly come to him — but the character's impact on the genre and all the slasher villains that came after him can't be overstated.
Where to watch: Amazon Prime