[1] The primary protagonists were schoolteachers Ian Chesterton and Barbara Wright, who provided the audience's point of view in stories set in Earth's history and on alien worlds.
The fourth character was the Doctor's granddaughter, Susan, who (though initially presented as an "unearthly child") was intended as an identification figure for younger viewers.
[2] Carole Ann Ford, who played Susan Foreman, became unhappy with the lack of development for her character[3] and chose to leave in the show's second series.
The intellectual Shaw was replaced by Jo Grant in the following season, and as the programme returned to occasional adventures in outer space, the format shifted once more: while UNIT continued to provide a regular "home base" for Earth-bound stories, in stories on other planets, the Doctor and Jo became a two-person team with a close, personal bond.
In 1974, the character of Harry Sullivan was created by the production team when it was expected that the Fourth Doctor would be played by an older actor who would have trouble with the activity expressed by his predecessor.
[7] During the Doctor's latest incarnations, his primary companions, such as Rose Tyler and Martha Jones, have fulfilled a distinct dramatic role, more significant than other, less prominent TARDIS travellers such as Adam, Jack, and Mickey.
In the first two series of the renewed programme, the only supporting actor to receive a title credit is Billie Piper, although short-term companions Bruno Langley (Adam Mitchell), John Barrowman (Jack Harkness) and Noel Clarke (Mickey Smith) all appear.
In "The End of Time", John Simm receives title billing for his antagonist role as the Master, ahead of Bernard Cribbins as companion Wilfred Mott.
In subsequent years, Claire Skinner, Nick Frost and Mark Gatiss have received title credits in special episodes for roles that are not considered companions, as does Piper for her non-companion return in "The Day of the Doctor".
In the revived era, some guest characters have gained companion status such as Mickey Smith, River Song, Wilfred Mott, and Craig Owens.
With the exception of Rory Williams (Arthur Darvill) and Ryan Sinclair (Tosin Cole), all regular companions have returned in some form for their Doctor's final episodes.
[19][20] Following her initial one-off appearance in "The Runaway Bride" (2006), Donna Noble (Catherine Tate) served as the primary companion throughout series 4, before returning again in the sixtieth anniversary specials (2023).
In "The Power of the Doctor" (2022), Tegan Jovanka (Janet Fielding) and Ace (Sophie Aldred) return to the series as one-off companions, with Ian, Jo and Melanie Bush (Bonnie Langford) also briefly appearing.
Companions Rose Tyler,[31] Mickey Smith,[32] Adelaide Brooke,[33] Amy Pond,[34] Rory Williams,[35] River Song[36] and Clara Oswald[37] have all been portrayed in their youths by juvenile actors on Doctor Who; the pre-companionship lives of the Pond-Williams-Song family being particularly well-documented.
For example, the loss of Amy and Rory Williams drives the Eleventh Doctor into solitude in Victorian London where he refuses to get involved in the world's affairs anymore.
[nb 1] Her death in "Face the Raven" leads the Doctor to undertake extreme measures to undo her fate, as depicted in the Series 9 finale "Hell Bent".
Steven Moffat, showrunner between 2010 and 2017, has stated that companion deaths are "wrong for Doctor Who", explaining that he does not believe the show should represent the "grittiness" of real life.
Several companions have been resurrected at some point in the series, including Jack Harkness, Rory Williams, Clara Oswald, and Bill Potts.
In Inferno, evil counterparts of Alistair Lethbridge-Stewart, Liz Shaw, and John Benton died in the destruction of their universe's Earth.
None of them have been featured on television, except for the mention of some Big Finish Productions original characters in the minisode The Night of the Doctor; however, some of them have passed from one media to another.