The "Alien" (sometimes referred to as a "Xenomorph")^[1][2] is a fictional endoparasitoid extraterrestrial species that is the primary antagonist of the Alien film series. The species made its debut in the film Alien (1979), and reappeared in its sequels Aliens (1986), Alien 3 (1992), and Alien Resurrection (1997), as well as the crossover franchise Alien vs. Predator (2004, 2007). A similar creature of a slightly different design also briefly appears in the Ridley Scott film Prometheus (2012). In addition, the Alien appears in various literature and video game spin-offs from the franchises.^{[citation needed]}
Unlike many other recurring enemy extraterrestrial races in science fiction, the Aliens do not have a technological civilization, but are predatory creatures with no higher goals than the propagation of their species and the destruction of life that could pose a threat (the film Prometheus implies they were engineered as a biological weapon by an advanced race). Like wasps or termites, Aliens are eusocial, with a single fertile queen breeding a caste of warriors. The Aliens' biological life cycle involves traumatic implantation of parasitic larvae inside living hosts, which mature before erupting from the host's chest. Their design deliberately evokes many sexual images, both male and female, to illustrate their blurring of human sexual dichotomy.
The Alien design is credited to Swiss surrealist and artist H. R. Giger, originating in a lithograph called Necronom IV and refined for the series' first film, Alien. The species' design and life cycle have been extensively added to throughout each film.