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"He was a candidate for a Midwestern congressional seat, and he hired me to manage his campaign advertising. Unfortunately, his opponent turned up something in his past with which we could not cope."
"Let me guess: he was secretly a liberal."
"Worse. An alien."
"You're kidding?! An undocumented alien running for—"
"No. A space alien, Ms. Walters."
Sensational She-Hulk #11, Jan. 1990

A character of extraterrestrial origins. For tropes about what makes them alien, at least from a biological standpoint, see Bizarre Alien Biology.


If you thought it meant "illegal aliens" and signed up, click Race Tropes. For interspecies romantic or sexual interactions, see the Interracial and Interspecies Love Index.

If there are no aliens at all, see Absent Aliens.

Compare Fantastic Sapient Species Tropes. Not to be confused with Otherness Tropes, though there may be some overlap.


Levels of the ladder of alien strangeness:

  • Sliding Scale of Anthropomorphism: This page contains a general list of ways that extraterrestrial characters can range in appearance, from humanlike to more alien.
  • Human Subspecies: Aliens who are related to humans.
  • Human Aliens: An alien which looks, sounds, and to some extent, acts human.
    • Human Outside, Alien Inside: An alien that looks like a human on the surface, but has some wacky parts and whatnot inside their body.
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  • Not Quite Human: An alien that is practically the same as a human except for one difference.
  • Rubber-Forehead Aliens: An alien whose face is significantly different from a human's, but only their face.
    • Green-Skinned Space Babe: An alien woman who looks like a human except for one or two obvious differences, and who at least one person in the main cast is attracted to if she's not just Ms. Fanservice.
    • Space Elves: Aliens who think they're superior (or might even be superior in some cases) to us, and act like a fantasy race.
  • Humanoid Aliens: Aliens who are humanoid, but don't look human.
    • Fish People: Underwater aliens, who are humanoids but look sort of like fish.
    • Frog Men: Humanoids that look and act rather like frogs.
    • The Greys: Grey, usually naked, short, humanoid aliens with large heads.
    • Little Green Men: Short, green aliens who drive flying saucers, and usually have antennae.
    • The Reptilians: Aliens that look like humanoid reptiles.
    • Intelligent Gerbil: An alien that's basically like a sapient, bipedal version of an Earth animal.
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  • Angelic Aliens: Graceful aliens that look sort of like humans and are seen as extremely beautiful.
  • Alien Fair Folk: Aliens that look like fantasy creatures from Earth's folklore (fairies, gnomes, trolls, goblins) or fantasy creatures who pretend to be aliens.
  • Little Green Man in a Can: Aliens that you can't tell what they look like as they all wear strange outfits.
  • Mechanistic Alien Culture: Aliens that are organic, but act like robots and have very tight schedules.
  • Insectoid Aliens: Aliens based on Earth bugs.
  • Alien Animals: Aliens that look exactly like Earth animals.
  • Sand Worm: Giant alien worms that live in the desert.
  • Starfish Aliens: Aliens that are radically different from humans.
    • Octopoid Aliens: Aliens that look like squids, octopi or jellyfish.
    • Tentacled Terror: Tentacles are a common feature of aliens, octopoid or otherwise.
    • Living Gasbag: Floating aliens that are literally full of gas.
    • Xenomorph Xerox: Extraterrestrials with the appearance and/or reproductive cycle of the eponymous creatures of the Alien franchise.
  • Mushroom Man: A creature that looks like a cross between a person and a mushroom.
  • Plant Aliens: Aliens that look like or are partly made of plants.
  • Blob Monster: Aliens that resemble shapeless blobs.
  • Silicon-Based Life: Aliens that are made of mostly silicon.
  • Telepathic Spacemen: Aliens with telepathy.
  • Mechanical Lifeforms: A race of robots or cyborgs that are treated as a real species.
  • Living Ship: A ship that's alive.
  • Energy Beings: Non-corporeal aliens.
  • Genius Loci: A sentient place.
  • Sufficiently Advanced Alien: Aliens that are so advanced that their technology seems like magic to humans.
  • Eldritch Abomination: An alien that just makes no sense.


Interspecies relations:



General tropes and other features:

Alternative Title(s): Space Alien