A team of researchers, isolated in a remote Antarctic station, discover a strange creature which has been buried in the ice for centuries. The Thing, as they come to call it, can assume the form of anyone, there is no way to distinguish friend from foe.
This fascinating idea formed the premise for Who Goes There?, a novella by John W. Campbell, Jr—published under the pseudonym Don A. Stuart in Astounding Stories in 1938.
Who Goes There? is a revisit of the classic gothic haunted castle story—you are trapped in the castle and a monster is in there with you. The films Alien and Poltergeist are two good examples of this sort of tale. But Who Goes There? featured a compelling plot twist: the monster could be anyone.
In 1951, Who Goes There? was adapted for the silver screen. Screenwriter Charles Lederer created a script with assistance from Howard Hawks and Ben Hecht (there was a rumour at the time, now discredited, that Orson Welles helped write the dialogue). Christian Nyby directed The Thing from Another World (with some guidance from Hawks) , starring James Arness as the titular Thing. In those days (the same year as The Day the Earth Stood Still and five full years before Forbidden Planet), science fiction movies were mostly about bug-eyed monsters abducting pretty girls in silver suits. Campbell's story got a pretty severe re-write, a fact that has given three generations of fans cause to refer to this film as "the James-Arness-in-a-Carrot-Suit Movie" (Arness himself was rumoured to have first uttered the carrot line, and was so embarrassed about his part in the film that he reportedly did not attend the premiere).
Three decades later, John Carpenter assembled a talented cast and crew and created The Thing, which stuck much more closely to Campbell's original story. The film, while not a box-office success, set a standard for action-science fiction films.
Particularly after the movie adaptations, many critics and analysts assumed that this was a cold war paranoia story. We never know who the enemies are, they could look and sound just like us. They could even be our friends and relatives.
The actual truth behind the inspiration for this story is much weirder.
Campbell's family was cold and unloving, which is bad enough—but wait! It gets strange!
John's mother occasionally switched places with her identical twin sister. How or why she would play such a prank on her unsuspecting child, I can not say, but auntie was apparently a pretty nasty customer. Young Mr. Campbell could never be sure if it was regular mommy, or extra-cold fake mommy who was present that day.
Of course, this is very cruel, and left the poor kid confused and upset. A case could probably be made that this borders on psychological child abuse.
But we got a really good science fiction story out of it.
References:
All from my memory, I actually assumed it was an urban legend for a long time.
Verified through Wikipedia and a couple other miscellaneous internet sources