Marshall Thompson in It! The Terror from Beyond Space (1958)

The Film

In 1973, the first manned expedition to Mars is marooned; by the time a rescue mission arrives, there is only one survivor: the leader, Col. Edward Carruthers, who appears to have murdered the others! According to Carruthers, an unknown life form killed his comrades during a sandstorm. But the skeptical rescuers little suspect that "it" has stowed away for the voyage back to Earth...—IMDB Synopsis

Bonus feature: Kim Spalding

How can you not love old sci-fi's costume choice? One-piece with a zipper from the collar all the way to the crotch area... Plus the manly man, Mr. Thompson. Oh, this is what dreams are meant for!