It starts on the page. In this case, the page was written by a man named John W. Campbell. Campbell is known predominantly as the editor the literary anthology Astounding Science Fiction from 1937 up to his passing. This perch allowed him so much influence over the field of science fiction literature that Isaac Asimov called him, in his memoir, I, Asimov, "the most powerful force in science fiction ever." In 1938, Campbell wrote and published his novella Who Goes There? which told the story of a small group at an Antarctic research base who have to contend with a shapeshifting alien from outer space.
Like Jack Finney's The Body Snatchers, published some twenty years later, the alien in question is capable of replicating the bodies of its victims to the point that that the other members of the expedition don't know if they are talking to the original or a doppleganger. Fun fact! This may have come from a painful experience from Campbell's own childhood. Campbell's mother was one of a pair of identical twins. For some reason, his aunt, his mother's twin, did not care for young John much, and there were times when John approached his aunt, thinking her to be his mother, only to be coldly rebuffed.
That'll fuck you up.
Enter Howard Hawks, one of the greatest film directors of Hollywood's Golden Age, with such films as To Have And Have Not, The Big Sleep and Red River to his credit. It was the late 1940's and by now Hawks had his own production company, Winchester Pictures Corporation. Having noted the rise in popularity of science fiction pulp magazines in the waning days of World War 2, Hawks purchased Campbell's story and had screenwriter Charles Lederer adapt it.
Fun fact! Lederer was the nephew of William Randolph Hearst's paramour Marion Davies.
Lederer made several changes to Campbell's novella, relocating the story from a research base in the South Pole to an Air Force base in the North Pole. He also, for clarification, removed the alien's ability to take over the bodies and personalities of its victims and instead, replaced it with a big, Frankensteiny dude in a space suit played by 6' 7" future Gunsmoke star James Arness.

James Arness' stunt double gets the Spinal Tap Stonehenge treatment
According to a 2020 article on the film in American Cinematographer magazine by George E. Turner, the film encountered a bizarre pushback in a normally mundane area. It was common for movies involving the military to get assistance and official sanction from the military, provided of course the military branch in question is shown in a decent light. Hawks had made several films, including Sgt, York and Air Force, that were all completed in cooperation with the Defense Dept. But when Hawks brought The Thing to the Air Force's attention, the same Air Force that ok'd the film Air Force turned them down. The reason bizarre was stated in the rejection letter, which was reprinted in the American Cinematographer piece:
"The script of Winchester Pictures' proposed production The Thing has been reviewed, and it is regretted that we will not be able to extend cooperation as the story revolves around flying saucers and their possible contents.
The Air Force has maintained the position for some time that there are no such objects as flying saucers and does not wish to be identified with any project that could be interpreted as perpetuating the myth of the flying saucer. Also, the Air Force seriously objects to any mention of Air Force personnel and equipment, or pictorial sequences representing Air Force personnel or equipment, being included in the film.”
Jesus dude, take a breath. Touch some grass.
Hawks went ahead with the film anyway, cooperation be damned. He hired his longtime editor Christian Nyby to direct, although there has been an ongoing debate in film circles as to whether Nyby really did direct it. Hawks was on set constantly and was a very “hands on” producer, not shy about relating his thoughts to Nyby about how the story should be shot. The general consensus, based on comments of the cast, etc., is that Nyby did indeed direct the film, but Hawks was always there, making sure Nyby directed the film the way he wanted it directed, to put it... vaguely.
The title was changed from Campbell’s Who Goes There to the more science-fictiony The Thing. And so it was intended to stay until singer and radio personality Phil Harris (the Jack Benny Show and the voice of The Jungle Book’s Baloo The Bear) had just released a hit novelty record called The Thing. Harris’ The Thing tells the story of a young man who finds a mysterious box that has washed ashore at a local beach. He tries repeatedly and unsuccessfully to give the box away but cannot, based on its (never revealed, but obviously hideous) contents. In an effort to distance the film from Harris' wacky-but-enormously-popular song, the title of the film was changed to The Thing from Another World. Additionally, the studio sent a letter to all exhibitors pointing out that The Thing fro the film bore no relation to The Thing from the song.
The Thing From Another World went on to become a critical and commercial smash. The film ends with a warning at the fade out: "Keep watching the skies! Keep watching the skies!" This became that catchphrase for all of the Commie invasion paranoia sci-fi of the 1950's .
The Thing From Another World would also go on to be remade, some thirty-two years later, by Howard Hawks fan and Halloween director John Carpenter, starring former Disney child star, Kurt Russell.
John Carpenter’s The Thing - covered next - although hated by critics upon release - and I mean, HATED - would eventually be recognized as a classic, but long, long, long after it's release. The same fate befell Blade Runner, which was released the same day (!!!). 1982's The Thing would - eventually - become so highly regarded that in 2009, a prequel, also called The Thing, was made. So... The Thing (2009) is a prequel to The Thing (1982), which is a remake of The Thing (1951), which was about a monster that can reproduce itself.
Got it.