A xenomorph is a fictional extraterrestrial creature that serves as the primary antagonist in the Alien film franchise. The term "xenomorph" comes from the Greek words "xeno," meaning strange or foreign, and "morph," meaning form or shape15.

Xenomorphs are parasitic, hive-based creatures with a complex, multi-staged life cycle that involves using living hosts for reproduction4. They are known for their biomechanical appearance, elongated heads, inner pharyngeal jaws, and blade-tipped tails15. Xenomorphs also possess a highly corrosive acidic blood that can eat through metal and other materials24.

The original xenomorph design was created by Swiss artist H.R. Giger for Ridley Scott's 1979 film Alien5. Giger's unsettling, biomechanical aesthetic, combined with the creature's predatory nature and adaptability, established the xenomorph as one of cinema's most iconic and terrifying monsters125.

Throughout the Alien franchise, xenomorphs have demonstrated the ability to adapt to their hosts' characteristics, resulting in numerous variations like the Predalien, Neomorph, and Deacon135. Despite these variations, the core attributes of the xenomorph - its parasitic life cycle, deadly abilities, and relentless nature - have remained consistent, cementing its status as a legendary figure in science fiction horror45.

The Xenomorph's origins can be traced back to the Engineers, an advanced extraterrestrial race first introduced in Prometheus (2012). The Engineers created a deadly black liquid capable of altering life forms and generating monstrous creatures1. It is theorized that the Engineers intended to use the Xenomorphs as biological weapons, with the black liquid serving as a means to create and control these relentless killing machines13.

The connection between the Engineers and the Xenomorphs was further explored in Alien: Covenant (2017), which revealed that the android David played a crucial role in the creature's development. After discovering the Engineers' experiments, David used the black liquid to conduct his own research on the planet, refining the Xenomorph into the iconic form first seen in the original Alien13.

The Xenomorph made its debut in Ridley Scott's Alien (1979), where it stalked and killed the crew of the Nostromo, leaving only Ellen Ripley as the sole survivor. H.R. Giger's surreal and nightmarish design for the creature, coupled with the film's claustrophobic atmosphere and psychological horror, established the Xenomorph as an instant icon of science fiction and horror cinema24. The film's success spawned a franchise that has expanded across multiple sequels, prequels, crossovers, video games, and comic books, cementing the Xenomorph's place in popular culture14.

The Xenomorph's physical attributes are central to its effectiveness as a biological weapon. One of the creature's most well-known features is its inner pharyngeal jaw, often referred to as the "attack tongue" or "foul tongue"3. This secondary jaw can rapidly extend and retract, delivering a powerful bite that can penetrate bone and metal3. The inner jaw is not only a formidable weapon but also serves as a source of food, as the Xenomorph uses it to feed on its prey's internal organs and fluids3.

Other notable physical attributes include the elongated cylindrical skull, which lacks any visible eyes, and the sleek black exoskeleton that is highly resistant to damage13. The exoskeleton is composed of polarized silicon, giving the Xenomorph an insect-like appearance3. Xenomorphs also possess sharp claws, spiked tails, and the ability to spit highly corrosive acid, further enhancing their lethality23.

The Xenomorph's physical form can vary depending on the host from which it emerges. For example, the Predalien, born from a Yautja (Predator) host, shares characteristics like dreadlock-like appendages, mandibles, and similar vocalizations2. The Runner Xenomorph, which emerged from a quadrupedal host, moves on all fours and has a more streamlined body structure3. This adaptability allows the Xenomorph to thrive in various environments and against different prey.