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.
Colin Baker
Colin Baker (born 8 June 1943) is an English actor. He became known for playing Paul Merroney in the BBC drama series "The Brothers" from 1974 to 1976. He later played the sixth incarnation of the Doctor in the long-running science fiction television series "Doctor Who" from 1984 to 1986. Baker's tenure as the Doctor proved to be a controversial era for the series, which included a hiatus in production and his subsequent replacement on the orders of BBC executive Michael Grade.