By circa 7700 BC, the Heitian civilization was dying out, having depleted the resources of their world through overpopulation and unchecked technological progress until only one city remained. They were unable to relocate to another planet as all technology had been outlawed.
When the king began dying, the head of the Science Ministry had him converted into a cyborg under his control. The cybernetic king decreed to his people that he would save them by taking them to another world, and that they would also be converted into cyborgs like himself. Three members of the Science Ministry were converted, but by that time the people were in open revolt. They mummified the four and sealed them away, allowing the Heitians to face extinction with their humanity intact.
In 2267, an archaeological dig conducted on Heitius VII by Dr. Stephen Mohr unearthed the mummified Heitians, who were reactivated and attempted to carry out their programmed missions to relocate to another planet and convert people into cyborgs, but they were stopped by the crew of the USS Enterprise, which transported them to the Federation Alien Life Studies Institute. (TOS comic: "The Mummies of Heitius VII")