2. Psycho (1960)
While Halloween is the greatest of the slasher films the slasher sub-genre itself would have no existence without the un-paralleled genius that Alfred Hitchcock displayed in his groundbreaking film Psycho. So many films have tried to reproduce the shock of Psycho while all have failed. Psycho was able to shock audiences by killing off its heroine, Marion Craine, in the first act of the film in a way that no filmmaker has been able to re-capture since. The film was also able to introduce new levels of violence and sexuality that had never been witnessed in film at the time to disgust and repulse audiences. The fact that Psycho is rather tame by today's standards only reinforces its influence by showing how copied it has become. If you want to see how shocking Psycho was at the time, then just watch any movie made before it came out. Psycho is also vastly important because it gave the film world the idea that the "monster" could be anyone and that sometimes the "monster" is something that can be found in everyday life. Hitchcock was able to put the fear and paranoia outside of the theater and into everyday life which is an accomplishment that has influenced every horror film that came after Psycho.