13. And finally… Freema Agyeman
Yep, you read that right, and no, we haven’t got confused. While Agyeman did reprise her Doctor Who role as companion Martha Jones for Torchwood, rather than star as a new character, technically she still qualifies for this list because she’d previously played someone else entirely in Doctor Who – Torchwood One worker Adeola, who was brainwashed by the Cybermen.
As was later revealed, Adeola was a cousin of Martha, so this reappearance at least makes total sense.