Star Trek: The Original Series, season 1, episode 7
What Are Little Girls Made Of?
Summary
In search of Nurse Chapel's fiancé, renowned exobiologist Roger Korby, the Enterprise visits the icy planet Exo III, where Korby has discovered an ancient machine that allows him to duplicate any living person with an android replacement. Korby plans to use the machine to spread controlled androids throughout the Federation, and replaces Captain Kirk with such a duplicate in an effort to take over the Enterprise.
Summary from Wikipedia, CC BY-SA 4.0.
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