38. The Abominable Snowmen

The Abominable Snowmen introduced the Great Intelligence and the Yeti to the Doctor Who mythos. Unfortunately only one episode of this story still exists. Another tragedy of this era. But in a lovely twist, Steven Moffet brought the Great Intelligence back in his recent Christmas special "The Snowmen", this time without the Abominable.

http://en.wikipedia.org/wiki/The_Abominable_Snowmen