Sarah Jane Smith
Sarah Jane Smith, played by Elisabeth Sladen, was a regular character on Doctor Who from 1973 to 1976, during which time she was a companion to the Third and Fourth Doctors.
Returned for a special appearance during the Tenth Doctor's 2006 series, for one episode.
Sarah Jane Smith was also the star of the failed spin-off K-9 and Company (1981), and is the lead in the more recent, ongoing Sarah Jane Adventures (2007).