Editing 1st Marine Expeditionary Force (section)

===Split one entity into good and evil entities===
In 2266, a strange ore had altered the function of the transporter, causing one of the most bizarre transporter accidents on record, 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 liquor, assaulting crewmen, and even attempting to rape Yeoman Janice Rand. 

When he was cornered, and finally captured in the engine room, his errant phaser shot damaged the transporter further. Scotty 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. 

Crippled with indecision, Kirk was able, barely, to make the trip, and his two halves were reintegrated once again. (TOS|The Enemy Within)

:''In the 1960s, the writers were encouraged to be vague about just exactly HOW Federation technology worked, so there were no detailed "rules" about what could and could not be done with it.  However, those established for the writers of "The Next Generation" made it clear that, like "Splitting one individual into two identical ones" below, this accident should not have happened.  This did not prevent them from having it happen anyway in TNG|Second Chances''