Alternative Character Interpretation: The original Expanded Universe novels (and the comic adaptations thereof) actually justify the propensity for humans to grab the Idiot Ball in the films by declaring that the Xenomorph Queens produce a telepathic broadcast which subtly enthralls humans, literally compelling them to subconsciously want to help the aliens breed and multiply.
Delusion Conclusion: While admittedly a pretty fringe theory, there is a section of the fanbase who were so dissatisfied with the later sequels that they would prefer to think that these were just nightmares Ripley had while in hypersleep.
While it may be due to the crossover between the two, both the Alien and Predator series have overlap thanks to both being '80s sci-fi horror series revolving around monsters, in addition to sharing numerous creators and actors between the two such as special effects by Stan Winston, James Cameron having input and actors such as Bill Paxton and Lance Henriksen.
Terminator has an overlap in interest with the series, owing to also being a violent '80s sci-fi series sharing numerous creators and actors with the Alien films, particularly several actors from Aliens and James Cameron. And the fact that both the Xenomorph and Terminator are guest characters for Mortal Kombat.
The Alien being inspired by parasitic wasps becomes incredibly funny when a new species of said parasitic wasp was named after the Xenomorph due to physical resemblance, and its especially brutal method of reproduction.
The first Dark Horse comic series mentions as a minor worldbuilding element that television broadcast equipment has become so compact and cheap that anyone could start a TV channel, which led to a collapse in viewing numbers. In the real world, the Internet has caused much the same thing. What was the cancellation threshold back in the eighties would be considered an enormous audience today.
I Am Not Shazam: The term "xenomorph" was originally just intended as a throwaway and deliberately cumbersome term for a generic alien life form, like the taxonomic equivalent of "UFO" (it literally means "foreign or alien form" in Greek). It was never intended as the name of the species itself; only to show up Gorman for being an officious twat. However, the name has proved easier for fans to use than "the aliens from Alien," and it's consequently been used in official marketing materials and semi-canon sources.
Iron Woobie: Ellen Ripley. In the first film, she's the sole survivor against a creature which killed her shipmates. In the second film, she gets demoted for destroying her ship in her attempt to destroy the creature, and in the extended cut, we learn her daughter grew up and died during her overextended time in cryo-sleep. When she's called back by her company to investigate the colony on the planet from the first film, she finds another Iron Woobie in Rebecca "Newt" Jorden, the sole child survivor of the colony's infestation. Ripley, Newt, Marine Cpl. Hicks, and the android Bishop are the only ones to survive and escape the Alien-infested colony, only for Ripley to be once again the sole survivor after they crash-land onto a prison planet in the third film; and having been impregnated with a Queen chestburster, her only option left is suicide.
The Alien series has a number of famous quotes that are frequently used outside of the film's context. They can be found on the films' YMMV pages.
On the receiving end of a number of memes making light of the fact that the franchise is now owned by Disney, such as showing the alien at Animal Kingdom or the Alien Queen as a Disney Princess.note ahem, Disney QUEEN. Or that, with the Alien Queen being, well, a Queen, all the rank-and-file Aliens are Disney Princesses.
Misaimed Marketing: The Alien is one of the creepiest, most disturbing and most sexual monsters ever invented and most of the films of the series contain enough gore and horror to scar kids for life. Yet, it hasn't stopped them from being merchandised, both as toys AND plush aliens and chestburster aliens. The Kenner toyline had such variations as Bull, Mantis, Crab and Jaguar aliens, making it one of the few toylines based distinctly around Bizarre Alien Biology.
Depending on your sensibilities, the overly genital-based based designs of the aliens can serve to make them look scary, or just plain silly and hard to take seriously as antagonists.
Narm Charm: There were plans, believe it or not, to make an animated kid's cartoon about Aliens vs Predator. While it never went through, parts of it did make it into a comic book series made for the Kenner action figures, which had Ripley and most of the marines from the second film surviving Acheron, and subsequently going on GI-Joe style missions to battle Aliens throughout the galaxy, wearing brightly colored uniforms, sprouting endless one-liners note "HUG THIS!" and wielding goofy, cartoonish weapons (Ripley wields up a flamethrower that's bigger than she is). One predator even appears to be wearing nipple cannons. When compared to the dark and gritty terror of the film, the whole series is hilarious (read it here).
Sequelitis: Notably avoided by Aliens, a great sequel which is widely considered to be as good as the first film. The third and fourth installments, and especially the AvP films, however, are considered a major step down. This is largely explained by the reasoning why the films were made. James Cameron was a fan of the original Alien and wrote the script to Aliens on spec. He was told that if The Terminator was successful he'd be allowed to direct the sequel he wanted to create, making it a labor of love. By Alien 3, however, the producers (who had meddled with the script of the first film) were making a sequel for the sake of the franchise. As such they burned through a bunch of different scripts and ended up with an amalgam of different attempts. Things didn't get any better from there. A number of people view that Resurrection might have been a pretty good film (a beloved screenwriter and a notable director with a solid grasp of visual style and atmosphere) if it hadn't been shoehorned into the Alien universe.
Viewer Gender Confusion: The Aliens themselves, especially the Queen who is often called a "she" in the films. Technically, all members of the species are hermaphrodites (i.e. having both male and female sex organs) from a visual viewpoint, because H.R. Giger's design is neither male nor female but a disturbing combination of both sexes. From a reproductive viewpoint, the series tends to flip-flop between the Aliens being actual hermaphrodites (Giger's own original portrayal of the creature included human-like sexual organs, a scene deleted from the first movie had the alien being able to "convert" two humans into huge eggs with fully-grown aliens developing inside, the original design for the Newborn from Resurrection was that it was, like Giger's original model, possessed of a human-like vagina and penis) and the Aliens being asexual "drones" where selected individuals can mutate into/be hatched as parthenogenetically fertile female "queens".
He's a strong android with medical knowledge, so he could have killed Ripley in three seconds if he really wanted to. Instead, when he moves against her, he starts flipping his shit and acting all deranged. Many viewers take this as indication that he's suffering from a programming conflict: he's supposed to help humans but his orders are to sacrifice the crew if necessary. His later comment on the alien being free from "delusions of morality" takes on a new light, then: he wishes he didn't have any sort of morality chip at all. And his distaste for humans can seem understandable when you consider that he is a slave, like other androids in the Alien universe. Why should he be expected to care for them? He isn't given much of a choice, either, and is just as much a victim of the Company as the other characters.
The other idea is that he actually is malevolent, beyond that which he is programmed for. The idea being that, in part, he is fascinated by the alien and wants to emulate it (That being the reason behind his method of killing Ripley), and actually has motives of his own, beyond simply studying the beast, indicating a degree of A.I. Is a Crapshoot.
Another idea is that Ash isn't working for the Company at all but for David. He is either a willing follower or was reprogrammed. It would explain his views on the Xenomorph and Humanity which are very much in line with David's.
Applicability: Ridley Scott said that there is no allegory, Freudian, feminist, Marxist, or otherwise to be found in this film. That has done nothing to stop decades of endless analysis of this film's use of H.R. Giger's excessively Freudian imagery and the role of Ripley as a feminist icon, among other things.
Best Known for the Fanservice: Ripley stripping down to some especially tiny underwear for little reason in the final scene. This has actually been used as a knock against the film's feminist bona fides, especially since the camera drops to crotch level throughout the whole scene. Scott seems to have been going for "vulnerable" - having her stripped down to just her underwear before she realizes the alien is still alive and on the shuttle and then suiting up in the armor-like spacesuit for the final confrontation - but he ended up with fanservice.
Common Knowledge: "The cast of the original Alien didn't know what was going to happen in the chestburster scene." Well, they knew, because they'd read the script, and it was described in a fair amount of detail there. What they didn't know was what it was going to actually look like, since no one had ever attempted an effect like it before, or the ins and outs of how it was going to be achieved. Everyone was sweating bullets that day. The effects team because they were trying to do something no one had ever done before and only had one take to get it right. The filmmakers because this scene was literally the only reason the movie got made, and if it didn't work or looked silly they were sunk. The cast because it was a big effects scene that would only get one take and they didn't want to be the reason it failed. There were hiccups, a few of which actually made into the movie. The first time they tried to ram the chestburster puppet through the fake John Hurt torso and shirt, it didn't work, and this "bulge" ended up in the film. Also, Veronica Cartwright (playing Lambert) happened to end up standing such that one of the blood jets hit her square in the face, her panicked squeal as blood sprays all over her is genuine (what didn't make it into the film is her falling backwards over a chair struggling to her feet and continuing the scene despite being basically in shock). But on the whole, the scene went as it was scripted and expected, the effect was just so radically new it affected the actors on basically the same level it affected the audience when the film was released.
Jones the cat. In the actual movie he barely has any screen time and when he does, all he does is hide, hiss and run away. (And constantly get the humans into trouble.) However the trailers and later TV Spots make it look like he's just as important as the Alien and Ripley. Considering how memorable he is, it's hard to blame them.
Among the human crew members, Parker the flamethrower-wielding mechanic.
Freud Was Right: The aliens, full stop. Also the Derelict ship, not to mention some scenes. It's H. R. Giger, what are you expecting? In fact, when it was suggested that any two roles could be played by women, Dan O'Bannon was adamant that the part of Kane not be one of the women, that the person who was facehugged and ended up getting chestbursted was a male, because he believed a woman in that position would be less scary, that it would "arouse [the male audience's] rape fantasies."
Dan O'Bannon: This is a movie of alien interspecies rape, that's it, that's scary, that scaring because it hits all of our buttons, all of our unresolved feelings about sexuality, all of them.
Ash assures Ripley that the dead Face-hugger isn't a zombie. Six years later, Dan O'Bannon goes off to write and direct The Return of the Living Dead.
In the novelisation, Ash says the aliens who left the distress signal to warn others from landing on the planet were a noble people, and that hopefully humanity will meet them under better circumstances. Come Prometheusthe Engineers are shown to have created the Xenomorphs as a Weapon of Mass Destruction, that at one point they attempted to use to destroy humanity.
Ridley Scott's preferred ending for the film involved the Alien killing Ripley and then mimicked her voice in her final transmission. Eight years later, the titular monster of Predator would demonstrate a similar ability.
Les Yay: Ripley and Lambert. In fact, one draft of the script actually had them as lovers.
Memetic Mutation: The tagline, "In space, no one can hear you scream," is one of the most famous taglines in film history, and is often parodied on other films' taglines.
Mis-blamed: Dan O'Bannon and Ron Shusett's original script had an all-male crew, with a caveat that the roles could be cast unisex. It also has—despite Giler and Hill's claims they did a page one rewrite—largely the same plot as the finished film. So all of the gender politics it's been lauded for (killing off Dallas so Ripley can become the Final Girl) and mocked for (Stephen King's allegation that Ripley rescuing Jonesy is sexist) don't actually exist, as the role was written as a man named "Martin Roby".
Moral Event Horizon: "Special Order 937," the company's plan to bring aliens to Earth, at the expense of the crew's lives. Given the events in Alien: Covenant, who actually wrote the order (David or an actual higher-up at W-Y) is open to interpretation.
When Parker and Lambert desperately try to wrestle Ash off of Ripley, there is this awkward moment where Ash grabs Parker's chest. It has the effect of Ash giving Parker a killer purple-nurple, though it does show that Ash is stronger than most humans.
When Ripley boards the escape shuttle, and finds the Alien in it. It appears to be napping in an empty nook on the wall, and it's reaching towards her without properly attacking reads like it's stirred, but not fully woken. At one point, it even slowly extends its iconic mouth tongue as if yawning. Until it actually starts attempting to attack Ripley, it's unclear whether it's stuck there.
The (thankfully deleted) extended opening, in which Kane stands in the breakfast nook and cheerfully namedrops every single character as they sit at the table. It's just as kitsch and embarrassing as it sounds. Ridley Scott must've thought so too, because he only filmed John Hurt's side of the scene before shelving it.
Lambert's slurred "Oh my god!" during the chestburster scene.
The baby Alien just zooming away after the chestburster scene. It's so fast and goes at such a straight line that it's comical.
The Alien's phallic head. For as blatantly Freudian as it looks, it's become an accepted part of the creature that most people have considered scary nonetheless.
The chestburster reveal manages to be scary in spite of some shaky effects due to the sheer gross out factor. There is a reason why the scene is so memorable.
Ash trying to kill Ripley by jamming a magazine down her throat is utterly silly on some level; it's not exactly clear how it will even kill her. But the performances from Holm and Weaver are strong enough to make it the disturbing pseudo-rape scene Scott intended.
Shocking Swerve: Ash being an android. While it's become so ingrained in pop cultural consciousness that nobody questions it nowadays, the existence of androids in the film's universe has zero foreshadowing and his robotic nature has zero bearing on the plot. He could've been swapped out with a creepy human and the story would've been functionally identical. Not to mention the incongruity of having completely lifelike robots with flawless speech recognition, logical processing, and voice synthesis, yet using monochrome command line CRTs and clunky mechanical keyboards to interact with the ship.
Signature Scene: The chestburster reveal, which paved the way for future Body Horror in science fiction. It's literally the only reason the movie got made (well, that and Star Wars had just come out, and Alien was the only sci-fi spaceship script anyone at Fox had laying on their desk). The producers thought the original script was horrible, but the chestburster scene was brilliant, and it was what got the movie greenlit.
The cuts between Ash's separated head and the dummy version are quite jarring. So much so that in the RiffTrax commentary, they say "Seamless!" in between cuts.
As Ripley is boarding the shuttle, she does an awkward turn and appears to fire her flamethrower, but the timing and the direction do not match the fireball she supposedly projects, and which continues burning after she turns her back to the corridor. While a viewer could chalk it up to the Nostromo itself exploding, the way it's staged imply Weaver missed her mark and the pyrotechnics people tried (and failed) to compensate for it.
At the end when the Alien is hanging outside of the ship and it's set against the white door and wall, it becomes too obvious the Alien is a man in a suit in spite of its high quality details, which is not helped by the fake looking spinning space background. The fact that it's a stuntman (necessary for the wire work involved) rather than the ultra-thin Bolaji Badejo in the alien suit might be a factor here as well.
Spiritual Adaptation: The film is an uncredited adaption of A. E. van Vogt's Space Beagle stories "Black Destroyer" and "Discord in Scarlet" - which did not go unnoticed by the author himself, who brought a lawsuit to 20th Century Fox that was settled out of court.
Tear Jerker: Parker's reaction to Brett's death, especially in a deleted scene where he and Ripley show up only seconds too late to save him.
Uncanny Valley: Ash, when his identity is exposed, moves in a stiff, deliberate manner, while also making twitchy, jerking movements. He goes into spasms when struck, and his wide-open eyes combined with the body movements just scream this trope.
Visual Effects of Awesome: The alien, despite how little we see of it until the very end. The creature is so well designed, at times, you have to remind yourself that it's actually a man in a costume.
The Woobie: Lambert, especially if you add in the Deleted Scenes. While she somewhat comes across as a whining bitch, she has a few establishing moments in the deleted scenes that paint her as a notably more sympathetic (if not necessary more likable) character, which makes her tragic demise even more gut-wrenching.
The 2019 Play
Big-Lipped Alligator Moment: The transition between acts 1 and 2 is Dallas jumping out of stage right while jamming on an electric guitar.