What was the first monster in Doctor Who?

Answer 1

The first is still the best... The Doctor's second story arc took him and his companions to Skaro, where they encountered the DALEKS.

Daleks are small, lizard like creatures with vestigial limbs, looking a bit like a slimy octopus. What makes them powerful is they 'ride' inside tank-like armored shells, never leaving them. Heavily armed and armored and, in later episodes shown to be capable of flight, these shells make the Daleks deadly.

Their 'motto' is summed up by their favorite word, "EX-TER-MIN-ATE!", as they have little to no tolerance for any other species.

In much later episodes it's revealed that the Daleks and the Time Lords are mortal enemies, and at some point they destroy each other in the last of the Time Wars.

Of course, the story of The Doctor spans all of space and time, and the Daleks are too cool to ever be completely destroyed, so they're not truly gone for good. :)