Sarah Jane Smith

Sarah Jane Smith is a fictional character in the British television series "Doctor Who" and its related spin-offs. She is played by Elisabeth Sladen. Sarah Jane was a companion of the Third and Fourth Doctor. 
She is an investigative journalist. Sarah Jane Smith is one of the companions who travelled the longest with the Doctor; Sarah Jane is also one of the most popular and well known companions. 
Sarah Jane appeared in two spin-offs: "K-9 and Company", and the as the main character of the ongoing series "The Sarah Jane Adventures". Sarah Jane also appeared in the new "Doctor Who" series with the Tenth Doctor ("School Reunion", "The Stolen Earth", "Journey's End").
History.
She first appeared in 1973 in "The Time Warrior", and then travelled with the Third Doctor. After the Doctor regenerated, she travelled with the Fourth Doctor. At the end of "The Hand of Fear", the Doctor had to go back to Gallifrey, where Sarah Jane was not allowed to go. Sarah Jane left the TARDIS and the Doctor, and returned to Earth.
Sarah Jane was a regular companion of the Third and Fourth Doctor, on the programme from 1973 to 1976 (seasons 11 – 14). She returns in the Fifth Doctor story "The Five Doctors" (1983), the 30th anniversary story "Dimensions In Time" (1993), and most recently in the episodes "School Reunion" (2006), and "The Stolen Earth"/"Journey's End" (2008), alongside the Tenth Doctor, and other companions of his era. The Tenth Doctor also featured in her own TV series "The Sarah Jane Adventures".