D is for... Delaware, Canton

Canton Everett Delaware III was an ex-FBI agent, who left the Bureau because of his sexuality. In the summer of 1969 he was lured back into service by President Nixon, after he began getting strange phone calls from a child direct to the Oval Office. It was as an old man, in 2011, that the Doctor's companions Amy, Rory and River Song first met him. He turned up at Lake Silencio in Utah after the Doctor had apparently been assassinated by a figure in a spacesuit who had risen out of the lake. He had been invited here after receiving a blue envelope just as they had. He brought petrol with which to burn the Doctor's body. An earlier version of the Doctor then took Amy, Rory and River to 1969 to meet the younger Canton in Washington DC, the TARDIS materialising invisibly in the Oval Office.
Canton accepted that the Doctor could help them investigate the child who was making the phone calls, and joined him in the TARDIS. Once it became known that the Silents had infiltrated the Earth, and had been here for centuries, Canton assisted with a subterfuge - appearing to capture the Doctor then to kill his companions. Searching for the child, Canton accompanied Amy to an abandoned children's home in Florida. She was abducted, but Canton shot and wounded one of the Silents which was taken captive. He recorded a conversation with the creature, part of which the Doctor then spliced into footage of the Moon landing - inciting people to turn on the Silents and kill them.

Played by: Mark Sheppard and William Morgan Sheppard (older Canton). Appearances: The Impossible Astronaut / The Day of the Moon (2011).

• The two Cantons are played by father and son, who between them hold an impressive number of genre appearances. Sheppard Snr, for instance, was the Klingon prison governor in the sixth Star Trek film, and also appeared in ST:TNG and ST: Voyager. He also featured twice in Babylon 5. Sheppard Jnr appeared in The X-Files first season, ST: Voyager, and became a regular on Battlestar Galactica and Supernatural.