Frazer Hines
Hines' "Doctor Who" debut came in 1966, when he was cast to play the part of Jamie McCrimmon, the companion of the Second Doctor (played by Patrick Troughton). Originally intended as a one-off guest character, Jamie joined the regular cast and appeared in the series from 1966 to 1969. Hines reprised the role in a cameo in the 20th anniversary serial "The Five Doctors" (1983) and as a guest star in "The Two Doctors" (1985). Hines would appear in 117 episodes of "Doctor Who" in all—more than any other "companion" actor in the history of the series. The only actors appearing in more episodes are those who played the first four Doctors. Many of the episodes featuring Jamie no longer exist in the BBC's collection.
Geoffrey Beevers
Beevers has made two appearances in the BBC science fiction series "Doctor Who", including as the third actor to play the Master in the serial "The Keeper of Traken", a role he has since reprised in some of Big Finish Productions' "Doctor Who" audio dramas ("Dust Breeding", "Master", "Trail of the White Worm", "The Oseidon Adventure", "Mastermind", "And You Will Obey Me", "The Two Masters", "The Light at the End", "The Evil One", "Requiem for the Rocket Men" and "Death Match"). Beevers narrated the unabridged audio edition of "Doctor Who: Harvest of Time", by Alastair Reynolds, released in June 2013. He also read the AudioGO (and later Audible) audiobooks of "Doctor Who and the Terror of the Autons", "Doctor Who and the Doomsday Weapon", "Doctor Who and the Sea Devils", "Doctor Who and the Space War", "Doctor Who and the Deadly Assassin", "Doctor Who and the State of Decay", and "The Ambassadors of Death"