Without a doubt, Alien (1979) is one of the most influential sci-fi films of all time. It spawned a series of sequels and semi-sequels (think Alien vs. Predator (2004) and Prometheus (2012)), inspired quite a few knock-offs, and encouraged filmmakers to create dirtier, grungier worlds for their sci-fi heroes to inhabit. But what inspired Alien? What movies passed their cinematic genes to Ridley Scott’s critically-acclaimed monster movie?

Well, Alien has quite a few parents, dating back to the paranoid thrillers of the 1950s. Screenwriter Dan O’Bannon was heavily influenced by Cold War sci-fi films like Invasion of the Body Snatchers (1956) and The Thing from Another World (1951) (“The Thing”), and if you watch these movies, you can find quite a few similarities. Take The Thing for example. This 1951 classic focuses on a group of soldiers and scientists living in an Arctic research station. They’re cut off from the rest of civilization, unwittingly bring a monster into their base, and when the creature awakes from hibernation, it goes on a killing rampage.

The monster (who’s essentially a walking vegetable) even uses its victims to fertilize its seeds. Sound familiar?

Director Ridley Scott brought along several influences of his own, including Tobe Hooper’s Texas Chainsaw Massacre (1974) (“Chainsaw”). While Scott wasn’t a big fan of horror films, Dan O’Bannon convinced the young director to give Chainsaw a shot. Evidently, Ridley was blown away by the horrifying spectacle as was producer Walter Hill. The story goes that Hill brought a hamburger and Coke to the screening, but he was so engrossed in the movie (or perhaps nauseated) that he forgot all about his food. Thanks to Chainsaw, Ridley Scott was inspired to create an edgy horror film that was basically a “haunted house” movie “in space.”

Two other films that left their imprint on Alien were 2001: A Space Odyssey (1968) (”2001”) and Star Wars (1977), probably the most important sci-fi movies of all time. Scott greatly admired the sets in 2001. They looked incredibly realistic, especially compared to earlier sci-fi films. However, Scott thought the world of 2001 had one little problem. It was all too clean, too perfect. And that’s where Star Wars comes in.

George Lucas’s space opera was a game changer, especially when it came to world-building. Star Wars took a science fiction universe and gave it that “lived-in” feel. Things were grimy and dusty, there were rooms full of garbage, and the droids were even covered in smudge marks. This gritty look inspired Scott to make the “Nostromo” feel like it was actually home to real human beings who lived there on a 24/7 basis. The sets were designed after B52 bombers and submarines, giving the “Nostromo” a very utilitarian feel, like it’s some sort of deep space oil tanker. The result is incredibly realistic and awfully claustrophobic, making the Xenomorph scenes even more terrifying.

Finally, the movie that had the biggest impact on Alien was actually a film that never made it past pre-production. Alejandro Jodorowsky, director of cult films like El Topo (1970) and The Holy Mountain (1973), wanted to adapt Frank Herbert’s Hugo-winning novel Dune (1965) into a film featuring the likes of Salvador Dali, Orson Welles, and Mick Jagger. Unfortunately for Jodorowsky, the movie fell apart, but that was great news for Ridley Scott. Out of work, several of the creative minds behind Dune migrated over to Alien, including conceptual designers Chris Foss and Jean Moebius Giraud, screenwriter Dan O’Bannon, and Swiss artist H.R. Giger, the man who created the facehugger, the chestburster, and the Xenomorph itself.

In other words, Jodorowsky’s loss was Ridley Scott’s gain…and ours too for that matter.