Doctor Who is a British science fiction television programme produced by the BBC. The programme depicts the adventures of a mysterious alien time-traveller known as "the Doctor" who travels in his space and time-ship, the TARDIS, which appears from the exterior to be a blue police box. With his companions, he explores time and space, solving problems, facing monsters and righting wrongs.

The programme is listed in Guinness World Records as the longest-running science fiction television show in the world and is also a significant part of British popular culture. It has been recognised for its imaginative stories, creative low-budget special effects during its original run, and pioneering use of electronic music (originally produced by the BBC Radiophonic Workshop). In Britain and elsewhere, the show has become a cult television favourite and has influenced generations of British television professionals, many of whom grew up watching the series. It has received recognition from critics and the public as one of the finest British television programmes, including the BAFTA Award for Best Drama Series in 2006.

The programme originally ran from 1963 to 1989. After an unsuccessful attempt to revive regular production with a backdoor pilot in the form of a 1996 television film, the programme was successfully relaunched in 2005, produced in-house by BBC Wales. Some development money for the new series is contributed by the Canadian Broadcasting Corporation (CBC), which is credited as a co-producer. Doctor Who has also spawned spin-offs in multiple media, including the current television programmes Torchwood and The Sarah Jane Adventures, and the 1981 pilot episode K-9 and Company.

The show's lead character is currently portrayed by David Tennant. In the programme's most recent series, which ran from April 5 to July 5 2008, Catherine Tate played the Doctor's companion, reprising her role of Donna Noble from the 2006 Christmas special. Another Christmas special will air in 2008, followed by four more specials in 2009; the next full series has been confirmed for airing in 2010.

David Tennant (born David John McDonald;; 18 April, 1971) is a Scottish actor. Already a well-known theatre actor, Tennant achieved wider fame for his TV roles in Casanova and Doctor Who, as well as his film role as Barty Crouch Jr in Harry Potter and the Goblet of Fire. He was ranked the 24th most influential person in the British media, on the 9 July 2007 MediaGuardian supplement of The Guardian. Tennant also appeared in the paper's annual media rankings in 2006.

The Fourth Doctor is the name given to the fourth incarnation of the fictional character known as the Doctor seen on screen in the long-running BBC television science-fiction series Doctor Who. He was portrayed by Tom Baker and is, as of 2008, the longest-running Doctor in Doctor Who history, having been on the show for seven continuous years (as opposed to the Seventh and Eighth Doctors who, although they each remained the "current" Doctor for more than seven years, did not spend that time on the air).