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.
History of Doctor Who
After actors Hugh David (later a director on the series) and Geoffrey Bayldon had both turned down approaches to star in the series, Verity Lambert and the first serial's director Waris Hussein managed to persuade 55-year-old character actor William Hartnell to take the part of the Doctor. Hartnell was known mostly for playing army sergeants and other tough characters in a variety of films, but Lambert had been impressed with his sensitive performance as a rugby league talent scout in the film version of "This Sporting Life", which inspired her to offer him the role.