Android duplicator
The android duplicator was a specialized piece of machinery discovered by Roger Korby in the underground caverns of Exo III around 2261.

Design 
Control of the duplicator was accomplished from a complex control panel, with precision controls that were color-coded but not otherwise labeled. This control center was located in a room adjacent to the duplicator itself.

The duplicator consisted of a large turntable that had slotted positions on either side of the turntable for the "blank" and "template"-being, both separated by a divider, and both with a locking mechanism placed mid-torso. On either side, paralleling the turntable, were two electronic components that were physically responsible for the duplication.

Use 
The android duplication involved two major stages in the process. 

The initial stage started with a "blank" and a naked human being, serving as the new android's "template", be loaded onto the turntable. The mechanism could create a physically exact duplicate of that being, including synthetic organs whose autonomic rhythms matched those of the template. While this platform spun at increasing increments of speed, the machine formed the blank into the android duplicate. At the conclusion of this process, the duplicate was only physically identical. No physical harm came to the "template"-being.

In the second stage, synaptic fusion, copied the target's thoughts and memories in the android. This stage also did not harm the original, but it was at least somewhat painful.

History 
The android duplicator was constructed centuries prior by the , the race that once lived in the planet's caverns, and was tended to for untold years by the android Ruk. With Ruk's help, and with records discovered by Korby, they were able to build . According to , he was constructed because the original Korby "had only [his] brain between life and death." It was also in this time frame that the android Andrea was also constructed, without an apparent source.

In the duplication process performed on James T. Kirk in 2266, he was able to interfere with the outcome of this stage by keeping an atypical thought in the forefront of his mind. Subsequently, the android responded to a comment from Spock with this thought, apparently without realizing it was something Kirk would not normally say. 

 claimed that if synaptic fusion was carried to conclusion, the original being's consciousness, or soul, could be transferred into the android duplicate. Such duplicates could then be programmed not to feel negative emotions or express negative traits. They formed the centerpiece of Korby's plan for a programmed utopia. Subsequent events revealed that the duplication process was not exact, and that the duplicates could, in fact, express traits other than those they were programmed to.

It was revealed that during Korby's duplication of himself, he had completely transferred his mind into it. Although the Korby android believed itself to be Korby, outsiders such as Kirk and Christine Chapel noted that its behavior was aberrant. Ultimately, Korby and all of the other androids were destroyed, leaving open the questions of when Korby actually died, and whether the Korby android was really Korby, or simply a machine convinced that it was Korby. ()

Background information 
The "android duplicator" was not identified by name in the episode, other than Korby's roundabout line about Ruk "still tending the machinery", or when the device was simply introduced as "this is how you make an android." Despite the lengthy description of the device in the script notes, emphasizing on the turntable, mention was made of the "squat "dynamo duplicators" at each end of the table glow and throb with power as Kirk's form and the mold form alternately pass."
Technology