Mondasian Cybermen

Specifically, the Mondasian Cybermen were designed and created by the humans of the planet Mondas, some of which became trapped on a giant colony ship contained within the gravity well of a black hole. The Doctor, Bill, Nardole and Missy discovered the ship and quickly deduced that because of the massive effects of the gravity of the black hole, time was moving faster at the top of the colony ship than it was at the bottom. This meant that any humans who found themselves at the bottom of the ship were dying more quickly and using up the ship’s resources more rapidly. This required the scientists and doctors on that level to begin developing technology which could supplement and replace their organic components as they began to fail or became susceptible to the toxic atmosphere on the ship. Experiments were carried out over a period of years on ‘patients’ at a hospital facility which slowly perfected the process of conversion. Eventually Bill Potts - who having been injured had already been brought to the lowest level of the ship and had a chest unit fitted - was fully converted. The conversion process was clearly very painful, but the head unit worn by completed Cybermen was specially designed to negate this.

Once enough people had been converted into Cybermen, their basic programming demanded that they seek out more humans for upgrading. Children were easier to convert, which is why a small army of Cybermen escaped the lowest levels of the colony ship and began to attack a band of humans that had settled on a solar farm in another part of the vessel. In a direct confrontation with the Doctor, the Cybermen were defeated, the Time Lord using the ship’s power systems as weapons against them. However, no one could be sure that all the Cybermen on the ship had been destroyed permanently.

And of course, wherever else there are humans with the technological capability, the rise of the Cybermen may yet begin again…