text: 1963–1973 William Hartnell, Carole Ann Ford, William Russell and Jacqueline Hill first appeared as the Doctor, Susan Foreman, Ian Chesterton and Barbara Wright respectively in the show's debut serial; An Unearthly Child. Ford departed in The Dalek Invasion of Earth in 1964 and was replaced by Maureen O'Brien playing a character called Vicki. Russell and Hill departed together the following year in The Chase and were subsequently replaced by Peter Purves as Steven Taylor. Adrienne Hill took over from O'Brien for a short period of time as Katarina. Jean Marsh subsequently played the character of Sara Kingdom also for a short period of time before being replaced by Jackie Lane as Dodo Chaplet in The Massacre in 1966. Purves and Lane stepped down from their roles at around the same time and were replaced by Anneke Wills and Michael Craze who played Polly and Ben Jackson.
  Patrick Troughton took over from Hartnell in the fourth season as the Second Doctor and starred alongside Wills and Craze and, after they stepped down, Deborah Watling, Frazer Hines and Wendy Padbury who respectively played Victoria Waterfield, Jamie McCrimmon and Zoe Heriot. At the end of The War Games, Troughton was replaced by Jon Pertwee who began his run as the Third Doctor alongside Caroline John as Liz Shaw in the 1970 serial; Spearhead from Space. John departed after Inferno and Katy Manning as Jo Grant, her replacement, appeared in the following serial Terror of the Autons. Throughout Pertwee's run, Nicholas Courtney, Richard Franklin and John Levene made regular appearances as The Brigadier, Mike Yates and Sergeant Benton respectively.