The first time I saw a theremin and knew what is was, was in the movie Forbidden Planet which is said to be loosely based on Shakespeare's The Tempest.
Strange instrument that must be incredibly difficult to master
It's actually not that difficult to master a Theremin, if you can hum or whistle a tune you'll be able to play one, because there's no visual reference to where the notes are, like on a guitar, you use your ears instead.