(coexisting on another dimensional plane)
The mirror universe was a morally reversed or "mirrored" reality parallel to the Prime universe.
Sometime before 1783 the British Empire was founded and began to spread throughout Earth like a plauge, earning them the nickname Black Death, by 2063 they had conquered the entire world and had evolved into the Terran Empire.
On 5th April 2063, the Vulcan ship T'Plana-Hath landed in Bozeman, Montana where they encountered Zefram Cochrane who rallied the other Terrans to board the ship, kill all Vulcans inside and raid their technology.
In 2155, the ISS Enterprise, under the command of Captain Maximilian Forrest, was the flagship of the Imperial Starfleet of Terran Empire. In January of that year, Commander Jonathan Archer mutinied against Forrest in order to take the ship into Tholian space to capture the primary universe starship USS Defiant which the Tholians had obtained. While the mutiny was ultimately unsuccessful, Captain Forrest had no choice but to continue the mission, since the ship's helm had been locked on auto-pilot. The Enterprise was later destroyed by Tholian ships, but not before Archer was able to take control of the Defiant. Archer tried to use the Defiant in a grab for power, intending to replace the Emperor, but was betrayed and killed by Hoshi Sato, who declared herself Empress. (ENT: "In a Mirror, Darkly")
In possession of the USS Defiant, the mirror universe was generally unaware of the primary universe. Knowledge of the primary universe and the Federation was restricted to the highest levels of the Terran Empire. In the primary universe, Section 31 had some knowledge of the mirror universe. (ENT: "In a Mirror, Darkly"; DIS: "Vaulting Ambition")
In 2256, the USS Discovery inadvertently traveled to the mirror universe via the Mycelial network. During this time, the Empire was at war with several rebel factions of Vulcans, Andorians and other aliens. Also, the ISS Buran's captain, Gabriel Lorca attempted a coup against the Terran Empire's Emperor Philippa Georgiou. The ISS Shenzhou under Captain Michael Burnham hunted Lorca down until both Lorca and Burnham were presumed dead. (Template:DSC)
However it was not until 2267 that any official contact between the universes is recorded. By this time, the Terran Empire was the dominant power in the Alpha Quadrant. In a transporter accident caused by interference from an ion storm, a landing party from the USS Enterprise switched places with an identical party from the ISS Enterprise in the mirror universe. The four Starfleet officers – Captain James T. Kirk, Lieutenant Uhura, Lieutenant Commander Montgomery Scott, and Doctor Leonard McCoy – found the Terran vessel to belong to an extremely brutal regime, almost dictatorial in its command structure. Advancement through assassination was commonplace.
During the encounter, Captain James T. Kirk convinced the counterpart of his first officer, Spock, that the Empire could not sustain itself. Indeed, Spock predicted that in its current form, the Empire had just over two centuries before total collapse. (TOS: "Mirror, Mirror")
Shortly thereafter, Spock rose to become leader of the Terran Empire, proposing a series of reforms designed to make the Empire more secure and less-dictatorial in nature. These included a significant disarmament program. Unfortunately, once these reforms were complete, the Empire was unable to defend itself against the equally aggressive and powerful forces surrounding it. The Klingon-Cardassian Alliance overran the Empire, conquering Earth and leaving Terrans and Vulcans enslaved. (DS9: "Crossover")
- Spock's rise to power is detailed in The Sorrows of Empire.
During this time, the forces of the mirror universe began implementing safeguards to prevent another crossover event with the primary universe. Transporter design was altered to prevent interdimensional travel, requiring the creation of devices specifically for that purpose, including the multidimensional transporter. In the event of another crossover, those involved would be killed to prevent further interference. (DS9: "Crossover", "Through the Looking Glass")
By the 24th century, the Terran Empire had been reduced to the Sol system and many had been taken as slaves, across the Galaxy many didn't even realise the Empire still existed. At some point a group of Terran slaves from Terrok Nor formed an uprising called the Terran Rebellion, after obtaining plans to a new type of warship, the Rebellion began to be a serious threat to the Alliance who were also fighting off the remnant of the Terran Empire. (DS9: "Crossover", "Through the Looking Glass")
By the 25th century, the Terran Rebellion had succeeded in throwing off Alliance rule and a reunified Terran Empire was once again a major power in the quadrant, possessing technology and weapons roughly on par with 25th-century Starfleet in the primary universe. Terran Empire ships and forces were known to operate in and around Cardassian territory, and even conduct missions to use the Bajoran wormhole to infiltrate the counterpart universe. (STO mission: "Crack in the Mirror")
The mirror universe had many different organizations.
- Terran Empire (Central government)
- Klingon-Cardassian Alliance
- Galactic Coalition
- Romulan Empire (replacement state)
- Xindi Council (mirror)
The Mirror Universe rarely includes some unique people distinct from the Prime Universe, these people include:
- Felix Fontaine (unique surname of Felix Knightly)
- Jake Sisko (born much later than prime counterpart, not genetic doppelganger)
- Adam Hilt (no counterpart in Prime Universe)
- Star Trek: Enterprise
- Star Trek: Discovery
- Star Trek: The Original Series
- Star Trek: Deep Space Nine
- Star Trek: New Horizons