On
stardate 1672.1, in
2266, a strange
ore altered the function of the transporter, causing a transporter accident in which Captain
James T. Kirk was split into two separate entities. One man embodied all of Kirk's so-called "positive" qualities and the other embodied all of his "evil" qualities.
It was some time before the mishap was discovered, and
the malignant version of Kirk roamed the ship, stealing brandy, assaulting crewmen, and even attempting to rape Yeoman Janice Rand. When he was cornered and finally captured in the engine room, the transporter was further damaged by an errant phaser shot he fired. Scott and
Spock isolated and repaired the damage.
Their repairs were confirmed when a test animal, which had previously been split in a similar manner to Kirk, was sent through the transporter in an attempt to reintegrate the two creatures. Upon reintegrating, it rematerialized dead, but McCoy speculated that this was the result of the animal not understanding what was happening to it and dying of fright, whereas the sentient and rational Kirk would be able to understand what was being done to him and thus be able to cope with it.
Though he was crippled with indecision, Kirk was able to make the trip (albeit barely), and his two halves were reintegrated once again. (
TOS: "
The Enemy Within")