Alien is a science fiction horror movie. Its main motive is to scare the audience. It relies on different elements for the scares then slasher films or psychological horror films. In a sci-fi horror film, the threats usually come from the unknown, or the alien. This can be taken in a literal sense or more abstractly. Science fiction horror can also encompass films in which the threat comes from technology. In Alien, the danger comes from a literal extraterrestrial, that is feared both for its dangerous abilities, and its unpredictable hostility. In a more practical sense, Alien falls into the science fiction sub genre because it is set in the future and takes place aboard a space ship.
The expectations and characteristics of sci-fi horror were vastly changed after the release of Alien in 1979. Prior to Alien, most sci-fi horror films were low budget B movies, most made in the 1950s. They played on fear of the other, a threat from outside. While the threats in these films often came from outer space, they often played on Americans fear of communism and the cold war. Some well known examples of this type of film Invasion of the Body Snatchers, The Blob, or It Came from Outer Space.
Alien introduced a new kind of sci-fi horror. The threat still comes from the unknown, and the mysterious, but there was more. Alien borrowed elements from other types of horror films, especially the slasher subgenre. Instead of a creepy old mansion where the characters were stalked by a serial killer, there could be a claustrophobic space ship where the characters were hunted by an alien creature. Alien uses the reveal of the tail or the head of the alien the same way a slasher film might reveal the killer’s knife while the victim is looking the other way. Alien uses a formula common to slasher films; a group of people are killed, one by one until the lead character, usually female, kills the killer. Alien managed to create a new and thrilling type of film by combining different elements of horror.
The killer sneaks up from behind in Psycho...
...An alien creature sneaks up from behind in Alien.
Science fiction is a genre of film that is usually dominated by male characters and male fans. By making the lead character Ripley female, the film makers expanded their potential audience. Alien became harder to dismiss as “just another sci-fi movie.” It also paved the way for more female action stars in science fiction and action movies (Sarah Connor in The Terminator, Trinity in The Matrix, Fry in Pitch Black).