; Date: Tue Apr 11 2017
The Daleks have been The Doctors longest-running enemy. They were people once, but a thousand-year-long war against the Thals forced them to remake their race into cyborg tanks intent on racial purity and being the superior race of the galaxy. Taking that to it's logical conclusion, the Daleks develop over time technological mastery way beyond anyone's imagination, but dedicated to the cause of wiping out all other inferior life forms.
The Tenth Planet
We first saw The Cybermen when an early space exploration effort saw a new planet in outer space. That was Mondas, the Cybermen home world, and a twin planet to Earth. "Twin" all the way down to the shape of the continents, except that Mondas was upside-down.
The Cybermen had been people, but embedded themselves in cybernetic suits and rid themselves of pesky emotions. Their planet was dying, and they wanted to colonize Earth or else suck energy from Earth in order to survive. Instead, the Doctor was able to force the destruction of Mondas
Another early space exploration involved a "Moonbase" occupied by humans, which was under attack from Cybermen.
The Wheel in Space
This was a deep-space research facility, wheel shaped to create an artificial gravity by keeping the wheel spinning. When the Cybermen come, it's not for a cup of tea and a chat. This is when Zoe joined the TARDIS crew, forming one of the iconic pairings of Jamie, Zoe and The Doctor.
The Tomb of the Cybermen
An archeological expedition to Telos is intent on uncovering the history of the Cybermen. Except that there's an ulterior motive, to reawaken Cybermen and use their power in a world-conquest-scheme hatched by a pair of ultra-logic-minded people who funded the expedition.
The Cybermen had retreated to cold storage in tombs on Telos due to some previous loss in battle.
Cybermats are small cybernetic creatures first seen on Telos in The Tomb of the Cybermen. They were later seen in The Wheel in Space, Revenge of the Cybermen, Closing Time, and Nightmare in Silver.