Rather than wasting time describing its parallel reality, The Original Series episode "Mirror, Mirror" lets a goatee, a scar, and a cruel smile speak for itself. This one brutal period set the groundwork long before Star Trek made the Mirror Universe a mainstay of the franchise.
After an ion storm and a transporter malfunction, Kirk, Uhura, McCoy, and Scotty find themselves aboard the ISS Enterprise, surrounded by doppelgangers who rule by intimidation, torture, and assassination.
A cunning transporter mishap becomes one of Trek's most significant episodes thanks to these distorted reflections, from Mirror Spock and his cold logic to Sulu's predatory swagger and Chekov's frantic power grab. With that being said, here are the best TOS Mirror Universe characters ranked.
5. Mirror Kirk
Mirror Kirk is less present on-screen than his crew, but his shadow hangs over every inch of the ISS Enterprise. We learn he’s secured command with the Tantalus field, uses assassination as a management tool, and has built a life where fear and desire are carefully weaponized against everyone around him, including Marlena.
What makes Mirror Kirk interesting is how the episode constantly invites comparison: the Prime Kirk spends the hour cleaning up the wreckage his counterpart has created while trying not to become him in the process.
By the end, when Kirk meets the Prime-universe Marlena and muses that she “seems like a nice, likable girl,” you can feel how narrowly his own life might have gone the other way if he’d been born under the Terran Empire’s banner instead of the Federation’s.