Re: Was TOS the first show to use the term 'parallel universe'?
I did see references to the concept at least as far as the Arabian Nights, and then there's ancient mythology with alternate planes of existence like Mount Olympus. It probably shows up in a Greek play or something too.
Curly: Moe, Larry, the cheese! Moe, Larry, the cheese! (Horses Collars, 1935)