It is unknown who portrayed them.
They have various altered forms, much different and recognizable from humans. Most are humanoid with greyish-green, hairless skin. They have a pronounced brow and deep set dark eyes below an undulating, vagina-like organ which may serve the purpose of a nose, mouth or both. While others possess octopus-like traits, such as tentacles. Their method of abduction is to appear in a blinding light and quickly whisk away their target. Due to this bright light and a loud screeching noise, those who encounter the beings are typically able to only catch a glimpse of their eyes, bodies, and long fingers. The purpose of their experiments on Pepper, Kit, Alma and Grace are currently unknown. Grace expresses the belief that their intentions are not malevolent.
Characteristics and Powers
- Transcendental Technology: Extraterrestrials possess highly advanced technological abilities, this allows them to perform feats that similar to magic.
- Space Travel: Extraterrestrials can travel from one place to another instantaneously.
- Resurrection: Extraterrestrials are powerful and advanced enough to restore a person to full life, despite their souls are delivered to afterlife by the angel of death, Shachath.
- Telekinesis: Extraterrestrials can psychically move objects and persons without touching them.
They seemingly abduct and experiment on Kit Walker and appear to abduct his wife Alma. They toss him in an isolated location in the woods that is coincidentally being used as a dumping ground for Bloody Face, where he is found by authorities. This results in Kit being tried and convicted of being the serial killer. His story of being abducted causes him to be transferred to Briarcliff Asylum, setting into motion the aliens' future interest in the facility. Early in Kit's imprisonment, Arthur Arden removes a piece of their technology, a spider-like microchip, from his neck, though he believes it is the work of communist agents. 
Arden tries to reintroduce micro-bot underneath Kit's flesh. During a storm (with lights in the sky that residents plead are not lightning), a drunk Sister Jude encounters a large alien-like being scurrying in a corridor of the asylum. She blacks out and later awakens in her office. 
Arden mentions that the chip had gone missing from his office several nights before. He believes it somehow got back into Kit but is unable to locate it.  They abduct Grace and subject her to forced abdominal surgery. Grace nearly bleeds to death from the procedure but is treated by Arden, who fears being scapegoated for the incident.  The aliens appear to Arden as he carries Grace's body out the death chute. They quickly take the body and disappear in a matter of seconds, leaving Arden shocked and confused. 
Arden concocts a plan to draw the aliens to Briarcliff. He makes a bargain with Kit, that he'll "kill" Kit with potassium chloride so the aliens will intervene to save him (as he deduces he is vital to their experiments) then reanimate him. While the aliens don't appear physically, their bright light begins to shine outside of Arden's office shortly after Kit's heart begins failing. Arden follows the blinding light into one of the cell rooms, where he finds Pepper along with a naked and pregnant Grace on the floor. 
Pepper reveals to Dr. Arden that the extraterrestrials have augmented her intelligence and placed Grace under their 'protection' so that she cannot be harmed. When the Doctor attempts to cut open her abdomen for a Caesarian Section, his scalpel flies out of his hands and he is thrown back. Contrary to his own opinions of himself, Pepper tells Arden that the Extraterrestrials are scornful of his experiments and consider him a joke. Later, Pepper acts as a midwife while Grace gives birth, an event witnessed and perhaps aided by Dr. Oliver Thredson, but Pepper neglects to inform him of Grace's abduction and return. Arden, wrought with feelings of inadequacy after what Pepper said to him and other events involving the possessed Sister Mary Eunice, would later go on to kill himself. 
Grace reveals to Kit that the Extraterrestrials are in fact kinder than human scientists, though equally as prone to mistake; she recalls the apparent death of Kit's wife Alma during a procedure involving watery submersion. She believes that her and Kit's child, which the aliens removed and then re-inserted into her, will have some special abilities gifted to it by the Extraterrestrials' modifications. Later, Alma shows up at Kit's old house, with another baby, presumably also fathered by Kit. 
Lana mentions that Kit was diagnosed with pancreatic cancer at 40, and one day just disappeared without notice. In actuality, the Extraterrestrials appeared while Kit was sitting in his home, and re-abducted him. 
While prepping Kit for exploratory neurosurgery, Dr. Arden notices a small lump in his neck. After making a small incision, he discovers what appears to be a microchip, an unknown technology to the era. After placing it on a tray, it sprouts six segmented "legs" and skitters away. The micro-bot appears to be almost indestructible, as it is able to autonomously reassemble itself after being dissected into several parts and welded by Arden, who believes its purpose to be espionage. Its current whereabouts are unknown but Dr. Arden believes that it has reintroduced itself to Kit's body.
Metaphor of God
According to Ryan Murphy and Tim Minear, aliens are the metaphors of God. Here’s an excerpt from producers Ryan Murphy and Tim Minear’s interview: 
Ryan Murphy: “For me, [aliens] were always an obvious metaphor for God. It fit very easily into the world of a Catholic sanitarium asylum... It was also about science versus faith so it made sense to me. The show is a show that pays tribute to a lot of horror masters. We take that seriously, so I always loved the alien idea of it, I loved what it was, I loved what it was about.”
Tim Minear: “The Betty and Barney Hill story of the fifties, sixties, was one of the first abduction stories. It was an interracial couple, we weren’t taking from that specifically, but it was in the water, in our experience, the stories that we all knew. When Ryan first pitched out that first story, he pitched it in that order, and he was like, ‘And then we meet him at his farm, and then he’s abducted by aliens.’ And my jaw was on the floor, but it felt exactly right to me for the period. If you think about it, those aliens are the closest things to angels, on our show about sort of religion versus science, there was nothing incongruous to me about any of that stuff.”
- The character most interested in making contact with the extraterrestrials is Dr. Arthur Arden, portrayed by James Cromwell; earlier in his career, Cromwell portrayed Dr. Zefram Cochrane in the film Star Trek: First Contact - another scientist whose work brings him towards the first communications between humanity and alien life-forms, though more reluctantly.
- Similarly, Zachary Quinto, who plays the dispassionate and logical Dr. Thredson, dismisses the existence of the extraterrestrials; Quinto recently gained notoriety for playing the dispassionate and logical alien Spock in J. J. Abrams' rebooted Star Trek film franchise.
- The extraterrestrials are responsible for restoring Sister Jude's sanity.
- With the exception of Julia and Thomas, anyone who has knowledge of the aliens' existence is either missing or dead.
- The aliens' true motive is still left unexplained.
- In a deleted scene of Asylum, a spider-like creature with a humanoid skull-like head can be seen behind Sister Jude's back.
- One of the extraterrestrials resembles Cthulhu, a famous fictional creature from the works of H.P. Lovecraft.
- ↑ Episode: Welcome to Briarcliff
- ↑ Episode: Nor'easter
- ↑ Episode: I Am Anne Frank: Part 1
- ↑ Episode: I Am Anne Frank: Part 2
- ↑ Episode: Unholy Night
- ↑ Episode: The Coat Hanger
- ↑ Episode: The Name Game
- ↑ Episode: Spilt Milk
- ↑ Episode: Madness Ends
- ↑ Entertainment Weekly, 'American Horror Story': Creators reveal secrets of 'Asylum'