Which character in the long-running TV series "Dr Who" can change form, allowing them to be played by a different actor?

Well yes - obviously the Doctor.   But also - the Master!!  

Yes, the Doctor's Gallifreyan brother-from-another-mother - himself a Time Lord - can also regenerate and has.  And yes, like the Doctor, he can sometimes be a she.

USQ popular culture researcher Dr Marcus Harmes grew up watching the first Master - played by the late Roger Delgado - and has just released a biography called "I Am Usually Referred to as The Master".  He's speaking with Phoenix Radio's Spencer Howson.