Season 4 The fourth season of " Doctor Who " ran between 10 September 1966 and 1 July 1967 . It starred William Hartnell as the First Doctor in the first two stories and then Patrick Troughton as the Second Doctor . Overview . Season 4 was a season of major changes for " Doctor Who " , including some that have influenced the series and franchise ever since . Most notably , season 4 saw William Hartnell ' s First Doctor hand off the baton to Patrick Troughton ' s Second Doctor in the very first regeneration . When Hartnell announced his plans to leave the series , the show ' s writers came up with the idea of having the Doctor change his appearance and personality . In 1966 , while it was not uncommon for actors to change in ongoing TV and film roles , this was possibly the first time a change in appearance was written into the very nature of the character . The regeneration ( a term that wasn ' t introduced until some years later ) occurred in " The Tenth Planet " , the second story of the season , which carried double significance in that it also introduced the Cybermen , a recurring menace that would quickly establish itself in a strong second - place position behind the Dalek s in the " Doctor Who " rogues gallery . As for the Daleks , an era ended with the series finale , " The Evil of the Daleks " , which at the time was expected to be the final Dalek story ever ( although a Dalek later made a cameo in 1969 ' s " The War Games " and the Daleks returned full - time to " Doctor Who " in 1972 ' s " Day of the Daleks " ) . The season introduced companion Jamie McCrimmon , one of the longest - serving and most popular TV companions . " The Highlanders " , broadcast this season , marked the end of the writers including occasional " historical serials " which featured no fantastic elements other than the TARDIS crew themselves . The next pure historical story would not appear until " Black Orchid " was broadcast in 1982 . For most of the season , the opening sequence , theme arrangement , and logo of the Hartnell era was retained . Beginning with " The Macra Terror " , however , a new opening sequence was introduced , and along with it a new series logo and a modified arrangement of the theme music ( introducing the " electronic spangles " sound and the tape echo effect that would both be retained through to 1980 ) . Most significantly , this new opening established the tradition of showing the current Doctor ' s face . Season 4 consisted of nine serials and forty - three episodes , the majority of which are considered lost ; this season has the sad distinction of being the only " Doctor Who " season for which not a single story survives in complete form ( although audio recordings exist for all the episodes which has allowed cassette and CD reconstructions of the stories to be commercially released . " The Power of the Daleks " and episode 4 of " The Tenth Planet " received animated reconstructions ) . It was during season 4 of " Doctor Who " that its long - standing rival , " Star Trek " , first aired on American television . Along with season 21 , it was one of only two seasons of the classic series to have a completely different cast in the final story of the season than in the first story . Adaptations and merchandising . Home media . Download / streaming availability . BritBox is available only in the US . iTunes stores carry " Doctor Who " serials in Australia , Canada , France , Germany , the UK and US , unless stated otherwise .