The Doctor (The Brain of Morbius)

Eight incarnations of the Doctor before the First Doctor were seen during the Fourth Doctor's mindbending contest with Morbius before the mechanism broke down. (TV: The Brain of Morbius, PROSE: Doctor Who and the Brain of Morbius, PROSE: Cold Fusion, AUDIO: Cold Fusion)

When Polly Wright, Ben Jackson, and Jamie McCrimmon found a shaving mirror on the control console of the second control room in the Doctor's TARDIS, Polly and Ben speculated that the room may have been used by a bearded incarnation of the Doctor from a time before either of the Doctors they were familiar with. (PROSE: Something at the Door)

Behind the scenes

 * A previous (TV: The Three Doctors) and later stories would suggest that William Hartnell's Doctor was, in fact, the earliest. (TV: The Five Doctors, The Time of the Doctor) However, the novel Lungbarrow proposed a possible solution: following persecution from Rassilon, a Time Lord founder threw himself into a Loom to be resurrected, and the Doctor had many of his memories.
 * According to Philip Hinchcliffe, who produced TV: The Brain of Morbius and himself appeared as one of the faces, "We tried to get famous actors for the faces of the Doctor. But because no one would volunteer, we had to use backroom boys. And it is true to say that I attempted to imply that William Hartnell was not the first Doctor." The faces included directors Christopher Barry and Douglas Camfield, script editor Robert Holmes, production unit manager George Gallaccio, producer Philip Hinchcliffe, writer Robert Banks Stewart, and production assistants Chris Baker and Graeme Harper. They all wore stock costumes.
 * Robert Holmes, who wrote The Brain of Morbius and appeared as one of the faces, would later introduce the idea of a twelve regeneration limit in TV: The Deadly Assassin. Assuming that the last face shown was the true first incarnation of the Doctor, that would have meant that the Fifth Doctor had no regenerations left. In Holmes' story TV: The Caves of Androzani, the Doctor said before his regeneration, "Is this death?" and "It feels different this time."
 * Lance Parkin, author of PROSE: Cold Fusion, confirmed that Patience's newly-regenerated husband was intended to specifically be the Douglas Camfield Doctor; in an earlier draft of PROSE: The Infinity Doctors, Patience's husband would have been the Robert Banks Stewart Doctor.