The 1979 Ridley Scott film that introduced the Xenomorph is Alien.
Alien follows the crew of the commercial starship Nostromo after they investigate a mysterious transmission and encounter a derelict spacecraft. An organism brought aboard develops through a horrifying parasitic life cycle, eventually hunting the crew inside the ship’s claustrophobic corridors. Sigourney Weaver stars as Ellen Ripley, alongside Tom Skerritt, Veronica Cartwright, Harry Dean Stanton, Ian Holm, Yaphet Kotto, and John Hurt.
The screenplay was written by Dan O’Bannon from a story developed with Ronald Shusett. Swiss artist H. R. Giger designed the creature and much of its biomechanical visual world, while Ridley Scott shaped the film’s slow-building tension and industrial atmosphere. Alien combines science fiction with horror and helped establish a lasting “haunted house in space” template.
The creature is commonly called the Xenomorph, but that name was not used as its specific name in the first film. In Aliens, Lieutenant Gorman uses “xenomorph” as a general term for an alien life-form. The first film simply calls it an alien or creature. Event Horizon, Predator, and The Thing are science-fiction or horror films, but none introduced this franchise’s iconic organism.