"It's Halloween. I guess everybody's entitled to one good scare."
— Sheriff Brackett
Halloween — a 1978 horror film directed and co-written by John Carpenter — serves as the Trope Codifier for the Slasher Movie formula.During the Halloween night of 1963 in Haddonfield, Illinois, six-year-old Michael Myers kills his sister Judith with a kitchen knife without explanation. Young Michael ends up committed to Smith's Grove Asylum and placed under the watchful eye of Dr. Samuel Loomis (Donald Pleasence). Fifteen years later — on the night before Halloween — Michael escapes the asylum during a blackout and heads for home, and Dr. Loomis soon follows in pursuit.Back in Haddonfield, high school student Laurie Strode (Jamie Lee Curtis) has a job as a babysitter for Halloween. As the night of the masks draws nearer, she keeps seeing an eerie masked figure stalking her. While Laurie and her friends believe a schoolmate has played a Halloween trick on her, Laurie has no idea of the danger waiting for Haddonfield...The film—#68 On AFI's "Thrills" list—became a massive success on its release and inspired countless other slasher films in its wake. It also spawned an extensive franchise and a remake/franchise reboot in 2007.
Halloween contains examples of the following tropes:
Cat Scare: Early in the film Laurie, walking home from school and having already caught a brief glimpse of Michael standing behind a hedge, is startled by Sheriff Brackett (who responds with the quote up top).
Later there's a scene where Loomis and Brackett are exploring the abandoned Myers house and a broken gutter suddenly crashes through a window, causing a startled Loomis to whip out a handgun.
Characters as Device: Michael does nothing but murder people, for which he gets no benefit and has no motive for. He's simply a monster to threaten our main heroine. It's intentional in this case, as Carpenter set out to make Michael impossible to sympathize with or even understand.
Color Wash: Cinematographer Dean Cundey used this to give the daytime scenes an autumnal brown tint and the night scenes an eerie blue one. (The 2003 DVD transfer of the film "fixed" this, much to the dismay of Cundey and the fans. Fortunately, the issue was largely rectified for the 35th Anniversary DVD/Blu-ray release in 2013.)
Deconstruction/Freudian Excuse: Inverted in Myers. Actually, never is justified or deconstructs Michael Myers's personality. While appearing to be a shallow motiveless-serial-killer movie at first, it is notable for how it stresses just how strange Myers' behavior actually is. Behind the scenes, Nick Castle (the man behind the mask) reportedly tried to figure out just what would drive a serial killer like Myers and act accordingly, but Carpenter specifically insisted on the "soulless killing machine" approach. One of the main characters, Dr. Loomis, is an experienced psychiatrist who is both baffled and terrified at the seemingly causeless evil lurking behind Myers' eyes. The overall idea is that, by any realistic standard, there should be a reason for someone to be anywhere near as warped as he is.
However, the two tropes are taken into account in the novelization of the film (from 1979).
Going by the Matchbook: Dr. Loomis finds a plumber's abandoned pickup, and in it is the same matchbook carried by the nurse who was with him when Michael Myers escaped the previous night; she left her matches in the car Michael stole, and they wound up in the truck of the guy he stole his jumpsuit from.
Things That Go Bump in the Night: The Shape (aka Michael Myers) is repeatedly compared to the boogeyman, apparently unkillable, and deeply enigmatic. He also seems to particularly target teenagers who are transgressive against social norms. In a subversion of this particular trope, he doesn't show much if any interest in actual children.
Time Skip: After the opening, the film skips from 1963 to 1978.
Trailers Always Spoil: The original theatrical trailer gives away the first scene's twist - that the killer is the victim's six-year old brother.