The 1982 John Carpenter film featuring an alien that mimics humans at an Antarctic research station is The Thing.
The extraterrestrial organism can assimilate living creatures and imitate them so convincingly that the American researchers cannot tell who is still human. This paranoia drives the film’s central conflict, especially after the team discovers evidence from a destroyed Norwegian base.
Carpenter’s film was adapted from John W. Campbell Jr.’s 1938 novella Who Goes There? It stars Kurt Russell as helicopter pilot R.J. MacReady and uses practical creature effects designed by Rob Bottin, which became one of the film’s defining achievements.
A common mix-up is confusing it with Invasion of the Body Snatchers, another identity-replacement story. The Thing is specifically set in Antarctica and centers on an alien organism that imitates individual organisms rather than replacing entire populations through pods.