text: 1973–1981 Katy Manning stepped down from the role of Jo Grant at the end of the tenth season in The Green Death. She was replaced by Elisabeth Sladen in The Time Warrior as Sarah Jane Smith. Jon Pertwee was subsequently replaced by Tom Baker at the end of Season 11 in Planet of the Spiders. Nicholas Courtney and John Levene reprised their roles as the Brigadier and Sergeant Benton numerous times during Baker's run. 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. After one more season, Sladen left the role of Sarah Jane Smith in the 1976 serial; The Hand of Fear. Louise Jameson debuted in The Face of Evil portraying a character called Leela. They were joined by K-9 in The Invisible Enemy, a robotic dog voiced by John Leeson and, on a few occasions; David Brierly.
  Jameson was replaced by Mary Tamm, who played Romana, a Time Lady and one of the Doctor's own species. Tamm stayed on for just one season before her character regenerated in Destiny of the Daleks and was portrayed by Lalla Ward. Baker, Ward and Leeson were joined by Matthew Waterhouse, the actor who played Adric, in Full Circle. Romana and K-9 departed together in Warriors' Gate. 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.
  1982–1996
  Peter Davison starred as the Fifth Doctor starting in the nineteenth season alongside Matthew Waterhouse, Sarah Sutton and Janet Fielding, before Waterhouse departed when Adric was dramatically killed off in Earthshock. In Mawdryn Undead, a new companion called Vislor Turlough was introduced, played by Mark Strickson. 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.