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.
Jacqueline Pearce
As well as appearing in the BBC children's programmes "Dark Season" (alongside Kate Winslet) and "Moondial", Pearce appeared in the "Doctor Who" serial "The Two Doctors" as Chessene, a bloodthirsty alien. She was associated with "Doctor Who" through her appearance in "The Fearmonger" as Sherilyn Harper, an audio drama by Big Finish Productions, and as Admiral Mettna in the webcast story "Death Comes to Time". Pearce returned once again to "Doctor Who" from 2015, this time opposite John Hurt, as a regular in the Big Finish audio series based on the adventures of the War Doctor, portraying Cardinal Ollistra, a leader of the Time Lords in the Time War who often clashes with the Eighth Doctor and the War Doctor over how far the Time Lords should be willing to go to achieve victory.