Doctor Who: 10 Best NuWho Guest Stars Ever

Given the amount of memes showing his character, a viewer new to the fandom could be forgiven for expecting Mark Sheppard to show up more in the new series. So far, he's had the one guest role in the Series 6 two-part opener The Impossible Astronaut/Day of the Moon, but the fact there's been a lot of clamour for him to return should give an indication of just how good he was.

He plays Canton Everett Delaware III, a former secret service operative recruited by President Richard Nixon to trace a mysterious call the President keeps getting from a young child. He meets up with the Doctor in the Oval Office and joins the TARDIS crew, heading off to investigate and running into the Silence as a result.

Sheppard plays the spy as impeccably cool, which is a big part of his appeal. He has the tough guy one-liners right down - "Welcome to America" on shooting a Silent, for example - and contributes to the TARDIS team dynamic by adding another interesting set of relationships for the other actors to play around with. Furthermore, he allows Canton's deeper issues. His conflicts with the system over his sexuality bubble under the surface, creating a deeper, rounded character for fans to love.