The Mirror Universe (MU) (Also referred in code as The Looking Glass) is a fiction parallel universe in which the plots of several Star Trek television episodes take place. It is named for "Mirror, Mirror", the original series episode in which it first appeared.
The characters in the Mirror Universe are generally the same as the characters in "normal" Star Trek continuity (for example, it has a James T. Kirk and a Spock), but their personalities are, on the whole, much more aggressive, mistrustful, and opportunistic. Whereas the Star Trek universe usually depicts an optimistic future which values peace and understanding, episodes set in the Mirror Universe show it to be marred by continual warfare, and compassion is seen as a liability. Uniforms are often more suggestive, such as women baring midriff.
Though the Mirror Universe is much darker and more violent than the normal Star Trek universe, a few Mirror characters are more friendly or docile than their "normal universe" counterparts. For example, Mirror Quark puts himself at risk to help escaped slaves reach freedom, and while "normal" Brunt is selfish and power-hungry, Mirror Brunt is a kind and considerate Ferengi.
There are an infinite number of parallel universes in Star Trek canon (as witnessed in the Star Trek: The Next Generation episode "Parallels"). However, the Mirror Universe is prominent among dimension-crossing incidents. The Mirror Universe has been visited in one episode of Star Trek, five episodes of Star Trek: Deep Space Nine, and two episodes of Star Trek: Enterprise, as well as in several Star Trek novels and several of the games (Star Trek: Shattered Universe, for example, takes place entirely in the Mirror Universe).
Read more about The Terran Empire (Mirror Star Trek) at Wikipedia
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Researched by: dustinprewitt