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.
Throughout Pertwee's run, Nicholas Courtney, Richard Franklin and John Levene made regular appearances as The Brigadier, Mike Yates and Sergeant Benton respectively.
The Fourth Doctor and Sarah Jane were joined on their adventures by Harry Sullivan, played by Ian Marter, before he left them in Terror of the Zygons.
The 1981 serial Logopolis was the first to introduce Sarah Sutton and Janet Fielding as Nyssa and Tegan Jovanka respectively, but the last to star Tom Baker as the Doctor.
Sutton stepped down from the role of Nyssa in Terminus and Kamelion, an unusual robotic character voiced by Gerald Flood, was introduced in The King's Demons.
For "The Five Doctors" – the show's 20th anniversary special – Carole Ann Ford, Nicholas Courtney, Elisabeth Sladen, Lalla Ward, Wendy Padbury, Caroline John, Richard Franklin, John Leeson and Frazer Hines reprised their roles as, respectively, Susan Foreman, Brigadier Lethbridge-Stewart, Sarah Jane Smith, Romana, Zoe Heriot, Liz Shaw, Mike Yates, K-9 and Jamie McCrimmon.
She was replaced in Planet of Fire by Nicola Bryant as Peri Brown, a serial which also marked the final appearance of Strickson and Flood.
The series was axed in 1989, but a TV movie was made in 1996 which saw Paul McGann taking over from McCoy and Daphne Ashbrook making her first and only appearance as Grace Holloway.
[4] Multiple actresses were considered to play the Doctor's next companion, with Billie Piper announced as the frontrunner to star as Rose Taylor.
[8] Due to disagreements with the producers and network executives, Eccleston departed after a single series[9][10] and was succeeded by David Tennant portraying the Tenth Doctor beginning at the end of "The Parting of the Ways.
[13] Elisabeth Sladen and John Leeson returned to Doctor Who in the series two episode "School Reunion" reprising their roles as Sarah Jane Smith and K-9, respectively.
"[20] Agyeman had previously appeared in a separate role in "Doomsday" and was cast as Jones following positive reception from the producers; the two characters were later explained to be cousins.
[24] Cribbins was not originally expected to appear outside of the special, but was asked to return in place of Howard Attfield who had portrayed Donna's dad Geoff and died unexpectedly while filming was still underway.
[30] The series four two-part finale saw numerous cast members return including Piper, Barrowman, Agyeman, Sladen, and Leeson,[31] while also featuring the departure of Tate.
[32] Tennant decided to leave the role following a series of specials[33] which featured David Morrissey, Michelle Ryan, and Lindsay Duncan as one-time companions in their respective episodes.
[40][41] Gillan previously played a soothsayer in the series four episode "The Fires of Pompeii" [42] Rory Williams was introduced as a recurring character portrayed by Arthur Darvill.
[52] Coleman made an unannounced guest appearance (as Oswin Oswald) in the series opener, "Asylum of the Daleks",[53] before joining the main cast from "The Snowmen".
[57] The first special celebrating the fiftieth anniversary of the series was titled "The Day of the Doctor" and saw the return of David Tennant and Billie Piper.
[58] Christopher Eccleston was initially set to return in the special as well but was later replaced by John Hurt, who played an incarnation of the Doctor not previously known.
[98] Walsh briefly returned in the episode as well,[99] with William Russell, Katy Manning, and Bonnie Langford portraying former companions Ian Chesterton, Jo Grant, and Mel Bush.
[111] Gatwa and Gibson will both continue their roles into the fifteenth series,[112][113] and are set to be joined by Varada Sethu,[114] who first appeared in the episode "Boom" (2024) as an unrelated character.