An incarnation of the Doctor, and identified as such by the Thirteenth Doctor's sonic screwdriver, hid out on Earth using a Chameleon Arch, going by the name "Ruth Clayton". This Time Lord had a history working for Gallifrey, in a role "[one did not] apply for", which she sought, though failed, to abandon.
She had her TARDIS buried near the lighthouse where she stored her true identity, and trusted Lee Clayton to protect her, under cover as Ruth's husband. Lee was also tasked with reminding her to "Follow the light and break the glass" when the time was right, as this would lead Ruth to return to the lighthouse, which she was made to recall from childhood, and finally restore her Time Lord memories. (TV: Fugitive of the Judoon)
Biography
Working for the Time Lords
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As Ruth Clayton
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Behind the scenes
This incarnation of the Doctor is the first within the DWU to be played by a non-white actor, although some stories have shown the Doctor briefly taking over the bodies of non-white humans, and others have indicated that non-white incarnations do exist somewhere along the Doctor's timeline.
Daniel Anthony played the Eleventh Doctor in The Sarah Jane Adventures story Death of the Doctor while he occupied the body of Clyde Langer, and Damian Lynch played the Third Doctor in the audio story Ghost in the Machine while he was using the body of Benjamin Chikoto to communicate.
More concretely, Russell T Davies' Rose novelisation shows that Clive Finch has collected photographs of, among other known incarnations, a tall, black female Doctor who wields a flaming sword.
In 1986, Lenny Henry also portrayed a parodic incarnation of the Doctor in a comedy sketch as part of his BBC series The Lenny Henry Show.