John Levene [born John Anthony Woods in Salisbury, Wiltshire, England] played Sergeant John Benton of UNIT on Doctor Who, beginning with "The Invasion" and concluding with "The Android Invasion."–TARDIS Index File, the Doctor Who Wiki
Matthew Waterhouse played companion Adric in Doctor Who from "Full Circle" to "Earthshock," with cameo appearances in "Time-Flight" and "The Caves of Androzani." After leaving the series, he began a stage career.–TARDIS Index File, the Doctor Who Wiki
Jacqueline Hill played Barbara Wright in Doctor Who from "An Unearthly Child" (including The Pilot Episode) to "The Chase." Hill has the distinction of being the first regular cast member of the series to actually appear on screen. She continued to play the role for nearly two years, leaving the show in 1965 but returning for an appearance in the 1980 Doctor Who story "Meglos," as the priestess Lexa.–TARDIS Index File, the Doctor Who Wiki
Nicholas Courtney (born William Nicholas Stone Courtney) played first Colonel and then Brigadier Alistair Gordon Lethbridge-Stewart, beginning in "The Web of Fear" and finally in "Battlefield." He reprised the role for the fan video Downtime (later adapted into one of the Virgin Missing Adventures), for the spin-off program The Sarah Jane Adventures, and for several audio dramas for the BBC and Big Finish Productions.–TARDIS Index File, the Doctor Who Wiki
Sarah Sutton played Nyssa in Doctor Who from "The Keeper of Traken" to "Terminus." She also made a cameo appearance as Nyssa in "The Caves of Androzani" and later reprised the role in the thirtieth anniversary special, "Dimensions in Time."–TARDIS Index File, the Doctor Who Wiki
Karen Gillan is a Scottish actress, who played the Soothsayer in The Fires of Pompeii, and plays Amy Pond, the first companion of the Eleventh Doctor, Matt Smith, in Series 5. The series began airing in the UK in April 2010.–TARDIS Index File, the Doctor Who Wiki
William Russell [born Russell Enoch in Sunderland, England] played Ian Chesterton in Doctor Who from "The Pilot Episode" to "The Chase." As one of Susan Foreman's teachers, he was one of the first of the Doctor's companions to appear in the series.–TARDIS Index File, the Doctor Who Wiki
Paul McGann played the eighth incarnation of the Doctor in the 1996 Doctor Who television movie and also voices the role in audio plays for BBC Radio and Big Finish Productions. His is considered to be either the longest or shortest tenure as the Doctor, depending on whether one counts the non-television stories to be canon or not.–TARDIS Index File, the Doctor Who Wiki
Matt Smith [born Matthew Robert Smith] portrays the Eleventh Doctor on Doctor Who. He made his debut in the part in The End of Time, Part Two, first broadcast on 1 January 2010.–TARDIS Index File, the Doctor Who Wiki
Billie Paul Piper [born Lianne Paul Piper] began her career as a pop singer in her teens, but is now best known for her part as Rose Tyler, companion to the Doctor in Doctor Who.–TARDIS Index File, the Doctor Who Wiki
Shadowcasts