Enter the Daleks
Sure, Doctor Who was a kids program with an ambition of teaching kids history. But the Doctor's Tardis was also a space machine, and to keep things interesting the next episode introduced the Daleks. Barbara is the first to encounter the Dalek though only the 'plunger' is seen initially, perhaps to add to the mystery of what could be so terrifying.
However, it is soon discovered the Daleks are not robots, but the mutated form of a once great civilization scared by the ravages of war. The only glimpse given of the mutated Dalek is a clawed hand coming from beneath a sheet Ian used to remove the mutant from it's casing. Perhaps not frightening by today's standards, in 1963 the Dalek became an overnight success.
The plot for the rest of the episode is used many times over in various episodes. The Doctor and Tardis crew are captured, they manage an escape but soon one or all are promptly captured yet again. Wash, rinse and repeat for several episodes. A rescue attempt is always mounted, usually with the aid of someone. In this case the Thals, the other sentient race on the planet.
Don't worry if you haven't heard of the Thals. They aren't seen again but once more, except maybe mentioned in passing. The Thals turned out much different than the Daleks. Instead of angry, hateful, war-mongering blobs, they have turned to peace and refuse to help the Tardis crew till Ian reminds them there are things worth fighting for. In this case a woman, what else?
Perhaps another cliché started is thinking they have destroyed the Daleks, for good. Of course this is used many, many times on all the various aliens the Doctor comes to encounter. As you might have guessed, it really comes down to how popular the particular BEM turns out to be. As mentioned above, the Daleks were a success and would return to torment the Doctor again and again.
WHO: The Daleks
PLANET OF ORIGIN: Skaro
GOALS: To exterminate all life in the galaxy that isn't a Dalek.
WEAKNESSES: Initially, stairs and a dependency on static electricity.
Next: Our dearly departed