The process of designing The Thing's titular alien monster was so difficult that one early plan would have killed the film completely. John Carpenter grew up a fan of '50s sci-fi movies like Forbidden Planet and the Quatermass films and was particularly enamored with 1951's The Thing From Another World. This adapted the short story Who Goes There? by John W. Campbell, about an Antarctic research base invaded by an alien creature that can imitate any living creature perfectly. The original film dropped that concept and instead made the monster (played by Gunsmoke's James Arness) a hulking, vegetable-based creature that resembled Frankenstein's Monster.

https://screenrant.com/thing-movie-john-carpenter-original-monster-form-plan-bad/