The Cybermen are just pipped to the post by the Daleks when it comes to monster appeal in Doctor Who. They first appeared in William Hartnell's last story "the Tenth Planet" and were the creation of Gerry Davis (who was script editor) and Dr.Kit Pedler (the scientific advisor on the show). As an aside, both men were intrigued by the idea of how technology could threaten life. (See Derek Wall.)
The Cybermen are basically hominids who replaced their ageing and decaying bodies with plastic and metal limbs, leaving only the brain, but a brain where "weak" features such as the emotions had been removed. Apart from gaining power, their other aim is to turn humans into Cybermen too.
Rather surprisingly, some have viewed this to mean the Cybermen are "communists" - what they mean by that are the varieties of Leninism which pervert notions of equality to such an extent that everyone should be the same. I have never bought that idea; the Daleks, on the other hand, are quite obviously based on the Nazis. No, the Cybermen are a nice bit of body horror; and the thing is, they are not too far-fetched either.
No-one gives a second thought to a pacemaker or artificial limbs these days; these inventions have helped numerous people to lead fulfilling lives all over the world. In fact, these days artificial limbs are at the meeting point of neuroscience, technology and medicine as there is research to develop artificial arms and legs that move and react like the real thing. It only takes a bit of imagination before you get to the Cyberman!
But what of the brain?
There is actually a concept called cybernetic immortality. And if the idea of computers storing our consciousness and creating a social superorganism raises an eyebrow, the idea of the human brain/computer interface is discussed at some length on sciam.com.
For the time being, the Cybermen are only to be found in Doctor Who (or the paler Star Trek version, the Borg). They are suprisingly closer to fact than any other monster in the show.
P.S. I just remembered the name - there is also something called "transhumanism". An example of this is here. Since my previous post on death, quoting Bladerunner, keeps popping up in Sitemeter info on hits to the blog, another quote comes to mind, in regard to all this: "I want more life, fucker!"