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- Chubby Oates
- Policeman, Planet of the Spiders (1974)
- Tracy-Ann Oberman
- Yvonne Hartman, Army of Ghosts (2006), Doomsday (2006)
- Maureen O'Brien
- Vicki
- Patrick O'Connell
- Ashton, The Dalek Invasion of Earth (1964)
- John Ogwen
- Bostock, Revelation of the Daleks (1985)
- Ardal O'Hanlon
- Thomas Kincade Brannigan, Gridlock (2007)
- Sophie Okonedo
- Liz 10, "The Beast Below" (2010)
- Kate O'Mara
- Rani, The Mark of the Rani (1985), Time and the Rani (1987)
- Colette O'Neil
- Tanha, Snakedance (1983)
- Stuart Organ
- Bazin, Dragonfire (1987)
- Michael Osborne
- Sorak, The Horns of Nimon (1979-1980)
- Sharon Osbourne
- Herself, The Sound of Drums (2007)
- Tony Osoba
- Lan, Destiny of the Daleks (1979)
- Kracauer, Dragonfire (1987)
- Glyn Owen
- Rohm-Dutt, The Power of Kroll (1978) - (1979)
- Daphne Oxenford
- Archivist, Dragonfire (1987)
Read more about this topic: List Of Doctor Who Cast Members