Mark Sheppard portrayed the younger version of Canton Everett Delaware III in the opening two-parter of series 6 of Doctor Who, The Impossible Astronaut and Day of the Moon. The older version was portrayed by his father, William Morgan Sheppard.
Sheppard's involvement with series 6 was greater in the United States, effectively being BBC America's "voice of Doctor Who" during the original run of the series. During 2011 he lent his voice to the documentary Doctor Who: Rewind, the behind-the-scenes series, Doctor Who Insider, several themed advertising campaigns (such as "Top Eleven for the Eleventh Doctor"), and most BBCA continuity announcements related to Doctor Who. His voice was always used to render the lines giving the time and day of an episode's broadcast.
Outside of the DWU Edit
Sheppard is also well known for the amount of tele-fantasy series he has appeared in, including The X-Files, Star Trek: Voyager, Firefly, Battlestar Galactica, Dollhouse, Warehouse 13 and Supernatural amongst others. He also had a recurring role in The Middleman, a Torchwood-esque action series which featured many references to the Doctor Who franchise.