Grant Matthews

In the mid 21st century, Captain Grant Matthews was one of only two humans that the Myloki duplicated, creating an indestructible version. The Second Doctor believed the copy was more of a Myloki-human hybrid since he seemed to be exactly like the original. Karl Taylor, on the other hand, was more like an animated corpse.

His Myloki programming was reversed, leaving him with free will. Decades later, the Myloki tried to retrieve him so they could sever their ties with our reality. The Doctor convinced him to go to them so he might find some happiness, since he had come to hate his immortality. (PROSE: The Indestructible Man)

Behind the scenes
* Grant Matthews is a reference to the title character of Captain Scarlet. Matthews (named to reference Scarlet's likeness to Cary Grant and being voiced by actor Francis Matthews), was reconstructed by the Myloki (Mysterons) so that he couldn't die. As a member of the organisation PRISM (Spectrum), the colour-coded officer's uniform assigned to him was scarlet. The war with the Myloki is started by Captain Karl Taylor (Captain Black) who is recreated as a Myloki agent.