Back when it started the show wasn't all about alien invasions, and serials such as Marco Polo saw the Doctor alongside various figures from Earth's past. In a purely historical rather than science fiction context, they combined entertaining stories with a subtle hint of education. Unfortunately the BBC recorded over many such early episodes in the mistaken belief that the tape they were filmed on was more valuable than the show itself. As such almost 100 "missing episodes" are no longer available in their entirety. Susan also became the first companion to leave the show when actress Carole Ann Ford was unhappy with her character's lack of growth. Although it could be said this decision was premature after only one year, she had appeared in over fifty episodes, and The Dalek Invasion Of Earth gave her a fitting farewell.
1965
With "Dalekmania" sweeping over Britain, a feature film was produced which allowed the Daleks to conquere the globe. An adaptation rather than a follow on however, Dr. Who and the Daleks retold the Doctor's first meeting with the fan favourites, and featured Peter Cushing as a human scientist who invents a TARDIS in his back garden. Not to be outdone the series carried on regardless, and the long succession of companions coming and going began in earnest: Ian and Barbara managed to return home (albeit two years late), while the Doctor was joined by Steven and Vicky. Mission To The Unknown was also broadcast in this year, a single episode which acted as a prologue to The Daleks' Master Plan, and the only episode ever to not feature either the Doctor, let alone the TARDIS or any companions.
1966
Audiences were in for a treat and a shake up when the TARDIS landed on The Tenth Planet. This specific serial was not not only the first to feature the now iconic Cybermen, but also introduced a rather ingenious solution to the problem of yet another cast member wishing to leave. William Hartnell's health (and disagreements with producers) got the better of him and the idea of regeneration allowed the popular show to continue without its lead actor, with Patrick Troughton taking over the role. Peter Cushing also reprised his own Doctor for the second and last time in Daleks' Invasion Earth: 2150 AD, this time joined by Bernard Cribbins.