2. The Daleks (1964)
For the Daleks, this is where it all started. The second story in the first season was our first glimpse of the Daleks with the cliffhanger ending to the first episode (Barbara being menaced by the mysterious plunger) being perhaps the most famous and still most effective cliffhanger in Doctor Who history. It isn't until the second episode that fans actually saw an entire Dalek for the first time, though. In these early days of the show, no one involved really expected the series to survive to the degree it has today. Ratings for its premiere episode, An Unearthly Child, were somewhat stunted by the unfortunate fact that it aired on the day of John F. Kennedy's assassination. However, ratings exploded with the first appearance of the Daleks, ensuring the continued survival of the programme and inspiring an entire generation of children to chase each other around whilst shouting "Exterminate" in a monotone voice. In their initial appearance, the Daleks are somewhat different than the ones that followed. In the base on Skaro, the Daleks are completely dependent on the electric current of their machinery in order to power their movement - they are powerless without it. As well as that, the First Doctor rather cruelly tricks his companions into exploring the Dalek City, not realizing they are all slowly getting radiation sickness. Not something the Doctor could do in a current adventure. This episode represents formative days for both the Doctor and his greatest foe but all the elements that make them fascinating are still present.