Mirror Universe
The Mirror Universe is the setting of several narratives in the "Star Trek" science fiction franchise, a parallel universe existing alongside, but separate from, the fictional universe that is the main setting of "Star Trek". It resembles the main "Star Trek" universe, but is populated by more violent and opportunistic doppelgängers of its people. The Mirror Universe has been visited in one episode of "", five episodes of "", a two-part episode of "" and a storyline in "", as well as several non-canon "Star Trek" tie-in works. It is named after "", the "Original Series" episode in which it  first appeared. Characteristics. The characters in the Mirror Universe are aggressive, mistrustful and opportunistic in personality. Whereas the "Star Trek" universe depicts an optimistic future in which the Earth-based United Federation of Planets values peace, co-operation and exploration, episodes set in the Mirror Universe feature the human-dominated authoritarian Terran Empire which values war, despotism and conquest instead. In "", it is stated that humans from the Mirror Universe suffer from photophobia (a sensitivity to light). Television appearances. Section::::"The Original Series". The Mirror Universe was first introduced in the original "Star Trek" episode "", which featured the brutal Terran Empire , managed by humans and their Vulcan allies, in place of the United Federation of Planets. The Mirror Captain Kirk of the ISS "Enterprise" was a mass murderer who was promoted to Captain after assassinating Captain Christopher Pike. Discipline aboard starships was enforced through agony booths and agonizers carried by crewmembers. Officers were barbaric in behavior and advanced in rank by killing superiors who they thought were incompetent. Nazi-style military salutes were used by crewmembers to show loyalty to their captain. The episode established the goatee as a visual marker for an evil version of a character. Section::::"Deep Space Nine . The Mirror Universe was later revisited in the " second-season episode ", and turned into a story arc that spanned into the final season, with five Mirror Universe episodes over the course of five seasons. The series reveals that when exposed to individuals from the normal universe, the Terran Empire began to reform itself for the better, but was overthrown in the 23rd century by an alliance of alien species who took advantage of the Empire's self-weakening and conquered it, enslaving humans and Vulcans in the process. Section::::Enterprise". A two-part episode of "", entitled "In a Mirror, Darkly", introduces  the early developments of the Mirror Universe. Section::::"Discovery". The first season of "" has a storyline involving the Mirror Universe. , commander of the USS "Discovery", is discovered to be an inhabitant of the Mirror Universe on account of his intolerance to bright light, a genetic trait common to all humans from the Mirror Universe. In 2018, Comic Book Resources rated "Discovery's" mirror universe saga as the 18th best multi-part episode story of "Star Trek". Appearances in other media. In addition to the television episodes, a number of ancillary tie-in works make use of the Mirror Universe setting. These  works may contradict continuity as established in the television episodes, and are not considered canon. Novels. Section::::"Star Trek: Stargazer". The "" novel "Three" by Michael Jan Friedman features the Mirror Universe. Section::::"Dark Mirror". The "" book "Dark Mirror", written by Diane Duane, offers another explanation of what happened after Captain Kirk and three of his crew encountered the Mirror Universe. In the novel, the Empire is still in existence in the 24th century. The point of divergence initially appears to be the Eugenics Wars where the genetic supermen were not defeated and eventually turned on each other resulting in atomic war, but  works dating back to the days of ancient Greece supporting the Empire's current mindset are noted. Section::::"Shatnerverse". Various novels have been set in the "Deep Space Nine" version of the Mirror Universe, including a trilogy by William Shatner, which reveals the Mirror Kirk (or "Emperor Tiberius" as he calls himself) is still alive and plotting to reconquer the Empire. Section::::"Star Trek: Mirror Universe". Two collections of Mirror stories were published in 2007: the first involves Mirror "", "" and "" and the second features Mirror "", "" and "". A third collection, entitled "Shards and Shadows", was released in January 2009. The Mirror Universe storyline  was concluded in the novel "Rise Like Lions", released in November 2011. A further story taking place in the Mirror Universe, "Section 31 - Disavowed", was released in October 2014. Games. A number of "Star Trek" games take place in the Mirror Universe or reference it. Among them, the first-person shooter "", the massively multiplayer online game "Star Trek Online", the battle simulator "" which is entirely set in the Mirror Universe, Decipher's Star Trek Roleplaying Game and "". Comics. "The Mirror Universe Saga" is a trade paperback that reprints eight issues of DC Comics' "Star Trek" comic book (issues #9-16 ) chronicling an encounter between the Mirror Universe and the Prime Universe. It is set immediately after the events of "". The series was written by Mike W. Barr and drawn by Tom Sutton & Ricardo Villagrán. This version postulates the divergence of history to start at the time of the Earth-Romulan War, with the conquest of Earth by the Romulans; after Earth's liberation, the resistance became an empire-building government. The concept of a morally inverted universe had been pioneered by DC Comics in 1964, three years before "Star Trek" adopted the idea, in the "Justice League of America" story  Crisis on Earth-Three written by Gardner Fox. Web series. The fan-produced web series "Star Trek Continues" included an episode set in the Mirror Universe called "Fairest of Them All".