Star Trek fans have selected the original series episode Mirror, Mirror as the top Mirror Universe story in the franchise.
The episode, which is season 2 episode 4 of Star Trek: The Original Series, first aired in 1967. It introduced viewers to a parallel reality where the crew of the Enterprise serves a tyrannical Terran Empire, with Captain Kirk played by William Shatner and Spock by Leonard Nimoy going undercover to return home. It remains the highest rated of 17 Mirror Universe episodes across the franchise, holding a 9.0 score on IMDb and topping Ranker polls with 46 first place votes from fans.