Martin appeared in last night's (January 26) episode, alongside Jodie Whittaker, who currently portrays the series's first female Doctor. Martin isn't necessarily taking over Whittaker's role, though.
The casting was unveiled in the latest episode, "Fugitive of the Judoon." Martin appears as Ruth Clayton, who is dramatically revealed to be a past Doctor.
"You're in my future, not the other way around," she tells Whittaker's character, the 13th Doctor.
Full details of Clayton's story and how she fits into the show's timeline have yet to be revealed.
Nevertheless, the arrival of a Black actor playing a Doctor has been received well by many fans on Twitter.
See some of their reactions below.
Dear @bbcdoctorwho @DoctorWho_BBCA Thank you for finally giving a Black nerd and other black nerdy adults and kids a Doctor who looks like us. You really dont know how monumental this was and how much it made me cry. Please don't let her be the only one ever. #DoctorWho— UzamakiJ (@UzamakiJ) January 27, 2020
Jo Martin IS The Doctor! 😍— Alex 🦉| Haruspis (@haruspis) January 26, 2020
Can we please, PLEASE keep her? Casting a WOC as Dr Who is a great choice - one I feared was still a long way off - but it really needs to be a concrete and substantial decision for the character, not a one-off thing for a series arc... #DoctorWho pic.twitter.com/r03HT9iW4t
Jo Martin as the Doctor!! Which incarnation exactly remains to be seen, and if she's even a canonical Doctor at all. All we know is she's the first black Doctor and in mere minutes she has OWNED the part!#DoctorWho pic.twitter.com/rIn7dBzEjx— Ryan Price-Stephens (@RyanPriceWho) January 27, 2020
we have our first black doctor I just realized-— Benni (@ArtsDalek) January 26, 2020
really happy this has happened because I hoped that after Capaldi we'd get a black doctor
welcome Jo Martin: you are the doctor (but, as we don't know which one, I'll name you the Random Doctor for now :) have nice day/night)