Rumors have been circulating that the series is ending, but only from tabloids so far:

http://www.sliceofscifi.com/2007/06/01/story-stating-end-of-doctor-who-absolute-rubbish/

The serial The Deadly Assassin established that a Time Lord can regenerate twelve times, for a total of thirteen incarnations (although at least one Time Lord, The Master, has managed to circumvent this). To date, the Doctor has gone through this process and its resulting after-effects on nine occasions, with each of his incarnations having his own quirks and abilities but otherwise sharing the memories and experience of the previous incarnations:

   1. First Doctor, played by William Hartnell (1963–1966)
   2. Second Doctor, played by Patrick Troughton (1966–1969)
   3. Third Doctor, played by Jon Pertwee (1970–1974)
   4. Fourth Doctor, played by Tom Baker (1974–1981)
   5. Fifth Doctor, played by Peter Davison (1981–1984)
   6. Sixth Doctor, played by Colin Baker (1984–1986)
   7. Seventh Doctor, played by Sylvester McCoy (1987–1989, 1996)[42] [43][44]
   8. Eighth Doctor, played by Paul McGann (1996)
   9. Ninth Doctor, played by Christopher Eccleston (2005)
  10. Tenth Doctor, played by David Tennant (2005–present)

Other actors have also played the Doctor, though rarely more than once (see the list of actors who have played the Doctor for details).

Dr. Who (Cushing) and his granddaughters, Susan (Tovey) and Barbara (Linden), show Barbara's boyfriend Ian (Castle) the Doctor's latest invention, a time machine called TARDIS.