Rupert Graves, best known for playing Inspector Lestrade in Sherlock, will be playing a character called 'Riddell' in episode 2 of Series 7. 

On speaking about his character, Graves said: “He’s a big game hunter … he’s in Africa, and there’s umm, some kind of history behind him and the Doctor, although it’s never fully explained what … he’s there to help the Doctor.”
This could confront rumors that the episode, written by Chris Chibnall, will be called 'Dinosaurs on a Spaceship'. On the possibility of the character returning, he said:  “I’ve no idea, no I don’t think there is actually.” Although Rupert Graves did not rule a return out: “Umm, I dunno … I’d have to see what they would be thinking of doing with the character.”

Rupert was sure about if he would like to play The Doctor himself: “No, I wouldn't like to be Doctor Who… No, I really wouldn't like to be in that kind of character at all…Once you get attached to one character in such a way, you never get any bloody peace then.”

Episode 2, featuring Rupert Graves, will be broadcast as part of Series 7 in the Autumn.

Source Interview Via DoctorWhoTV