Marya Morevna, the warrior princess from a Russian fairy tale The Death of Koschei the Deathless.
Art by me.
ok this made me look up the story of Koschei the Deathless partly cuz I was curious as to how, if at all, it ties into the Master’s real name being Koschei in Doctor Who
answered some questions raised others
on the one hand, “malevolent, death-cheating rival of hero in folktales” does seem to fit
on the other hand the “etymology” section is rather fascinating (there’s probably fan theories to be written about a guy whose name could mean “slave” taking the pseudonym “master”)