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.
The Two Doctors
This story marked the final appearance of Patrick Troughton as the Second Doctor and the final on-screen appearance of Frazer Hines as Jamie. The Second Doctor appearing much older in this feature, with noticeable grey hair, has been addressed in novelizations and audio books as there having been a significant amount of time passing between "The War Games" (1969) and the Second Doctor's regeneration in "Spearhead from Space" (1970).