The Doctor will have two assistants in the next series of Doctor Who. A new companion, expected to be announced soon, will join the Time Lord, played by David Tennant, for the entire fourth series of the BBC One revival, due to begin filming in southeast Wales next month. The latest sidekick, Martha Jones, played by Freema Agyeman will be absent for the first half of the series, but will be in the spin-off, Torchwood, starring John Barrowman, centre.

Doctor Who facts

The first episode of Doctor Who was broadcast on BBC 1 on November 23, 1963.

Ten actors have played Doctor Who, beginning with William Hartnell and ending with the current Doctor, David Tennant.

The longest serving Doctor was Tom Baker who played the part from June 1974 to March 1981.

The series was axed December 1989 and was not revived until 2005 when Christopher Ecclestone was unveiled as the new Doctor.

In 1996 a one-off Doctor Who film was broadcast on television. Starring Paul McGann, it was intended as a pilot for a new American-produced Doctor Who series. Although a ratings winner in the UK, it flopped in the US so no new series was made until the revival in 2005.

The Doctor Who theme tune, composed by Ron Grainer, was the first television theme tune in the world to be realised entirely through electronic means.

The original theme served, with minor edits, as the theme tune up to 1980.

The programme is listed by the Guinness World Records as the longest-running science fiction television series in the world.

The Daleks - mutated organisms integrated with a tank-like mechanical casing made of "dalekanium" - were created by writer Terry Nation and BBC designer Raymond Cusick and introduced in December 1963.

Other notable adversaries of the Doctor include the Autons, the Cybermen, the Sontarans, the Zygons, the Sea Devils, the Silurians, the Ice Warriors, the Wirrn, the Yeti, the Slitheen, and a Time Lord with a thirst for universal conquest known as the Master.

John Cleese, Martin Clunes, Leslie Grantham, Alexei Sayle, Windsor Davies, Peter Sallis and Richard Briers have all appeared in Doctor Who.

The show won a BAFTA Award for Best Drama Series in 2006.

TARDIS stands for Time And Relative Dimension In Space.

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