5 Timey Wimey Clues To Where Ruth Fits In Doctor Who Canon
These clues reveal how Doctor Who's newest mystery incarnation can exist.
Doctor Who series twelve episode five threw a curveball to the audience in revealing that the titular Time Lord actually has one more previously unseen past incarnation. Longtime viewers of the show will remember a similar revelation happening back in 2013 with John Hurt’s War Doctor.
In the Series Seven episode, The Name of The Doctor, as Clara fell through The Doctor's timeline she came face to face with an unknown (and to that point unaccounted for) version of the renegade Time Lord. This set the standard that The Doctor's past is not always as it seems and the numbering scheme we take for granted may not be accurate at all.
For the sake of convenience and sanity we still call Matt Smith the Eleventh Doctor and keep count as if nothing were different. However, now we are faced with a new face for The Doctor and like the previous example the audience has to reconcile the fact that her past is now more complicated and not at all what it was assumed to be.
However, while the War Doctor reveal took advantage of the story gap between classic Doctor Who and the revived series, this newest one has a small technical hitch: all of The Doctor’s past regenerations have been shown and accounted for!
5. Time Lords Can Selectively Wipe Memories
In the classic story, The War Games, the Time Lords arrested the Second Doctor and put him on trial for breaking the laws of time. One consequence of his capture was that they chose to selectively wipe the memories of the Doctor's two companions, Jamie and Zoe, erasing all but their earliest adventure with him.
It's worth noting that while The Doctor as a Time Lord has an inborn resistance to psychic attacks, he is not immune to having his memories altered. During the episode Time Heist he uses memory worms to erase his own memory and later in Hell Bent, Clara uses a Time Lord device to selectively erase his memories of her.
This is the most likely explanation for why the Thirteenth Doctor does not remember ever being Ruth. Because she once worked for the Time Lords in some covert capacity before going rogue, and when they finally caught up with her they did not want their secrets known to a renegade like The Doctor. They adjusted her memories to erase that entire incarnation.
Having successfully done this to The Doctor, it is possible that The Time Lords put The Master under the same kind of mind wipe and he took his revenge on Gallifrey after learning the truth.