The Doctor on Doctor Who has been traveling through time and space for thousands of years. And wherever he goes, he seems to find trouble. While the Doctor would be the last to admit it, he's a hero to many people (and aliens). Whether he is on Earth or another planet, whether he is visiting the past or the future, he's constantly doing what he can to save whoever needs saving. So like most heroes, he has plenty of enemies. His arch-nemeses might be the Daleks, but they are hardly the only species who are determined to defeat him. Fighting the Doctor for nearly as long, and just as viciously, are the Cybermen.
First introduced during the original series' fourth season in a story called 'The Tenth Planet', the Cybermen were originally humans living on the planet Mondas. They grew so physically weak that they began to replace their body parts with metal and plastic, until they eventually became the Cybermen -- half living, half machine, and completely without emotion. Convinced that being Cybermen was superior to being a completely biological being, they set out to convert every living person they found into more Cybermen.
Ever since they were first introduced, the Cybermen have continued to plague the Doctor, and have killed numerous humans and aliens by conscripting them into their robotic army. But they have not been the original Mondasian Cybermen in over 50 years. Instead, the Doctor has been facing creatures converted from other species. But according to the show's official Twitter account, the Mondasian Cybermen are finally making a comeback:
Guess who's back!
— Doctor Who Official (@bbcdoctorwho) March 6, 2017
The Mondasian Cybermen are a major part of Doctor Who history. Not only for being one of the Doctor's most frequent foes, but also because the story that introduced them -- 'The Tenth Planet' -- also introduced the concept of the Doctor's regeneration. At the end of the last episode in 'The Tenth Planet' story the Doctor was so exhausted by the struggle with the Cybermen that he died, and regenerated into a much younger body. This story allowed the original actor William Hartnell to be replaced by Patrick Troughton, thus ensuring that the show could continue on whenever the actor playing the role wanted to leave, or didn't work out.
Season 10 is the final one for both showrunner Stephen Moffat and current Doctor Peter Capaldi. With Capaldi on his way out the door, perhaps history will repeat itself and the Mondasian Cybermen will once again be responsible for the Doctor's next regeneration.
Doctor Who season 10 is set to premiere on April 15, 2017 on BBC America.
Source: Doctor Who Official