- This character is a member of Spock's family.
At the time the war between the United Federation of Planets and the Klingon Empire began, the USS Enterprise was mapping a region of deep space near the Shapley Center, and was thus cut off from the Federation. Captain James T. Kirk decided to go to Organia and investigate its apparent destruction, a journey which would take nearly six months. To save time, Montgomery Scott developed a way to modify the ship's transporter so that it could use tachyons to create a copy of Spock and beam him to Organia, after which he would return automatically to the Enterprise one day later, give his report, and revert back to tachyons.
After Kirk approved Scotty's proposal, the modifications were made to the main transporter room, the most prominent of which was the enclosing of the transporter chamber itself in a metal tank so that Hilbert space, the dimension in which tachyons existed, could be established inside. The experiment was carried out, but unknown to the crew, the thought-shield the Klingons had placed around Organia reflected the duplicate Spock back to the Enterprise -- he not only failed to reach his destination, but both his body and mind were reversed, altering his loyalty from the Federation to the Klingons. Kirk dubbed the two Spocks "Spock One" (the duplicate) and "Spock Two" (the original), and gave Spock One his Command Academy ring so he could tell the two apart.
Spock Two, sensing his counterpart's opposite nature and realizing the danger he posed, insisted to Kirk that Spock One be destroyed, while Spock One convinced him to keep both of them on as first officer on separate shifts until a way could be found to determine the duplicate from the original. Shortly afterwards, Spock One instructed the ship's computer to take them out of warp for a second so they could be detected by the Klingons, forcing Kirk to relieve both Spocks from duty. Spock One later barricaded himself in the medical lab, where he used the equipment and chemicals to synthesize the nutrients he needed to survive, since being a mirror duplicate he could not consume normal food. He refused to leave or help the crew solve the mystery of what happened to Organia unless Spock Two was destroyed, but upon hearing Leonard McCoy's announcement that he had found a way to determine which Spock was the duplicate and had already worked out that it was Spock One, he escaped from the lab and headed for the hangar deck. He stole a shuttlecraft Galileo II, modified its engine to make it warp-capable, and headed to Organia. Kirk, Spock Two and Scott followed him there, and the two Spocks engaged in a mental battle which resulted in Spock One's destruction. (TOS novel: Spock Must Die!)