Sarah Jane Smith

Companion of the Third and Fourth Doctors and a plucky British journalist.  Posing as her aunt Lavinia, she infiltrated UNIT to look into the mysterious disappearances of several important scientists.  SHe then stowed away in the TARDIS and found herself in the 12th-century, where she helped the Third Doctor defeat the Sontaran, Linx.  Afterwards, Sarah Jane helped the Third Doctor defeat Sir Charles Crover's Operation Golden Age, the Daleks, the ice warriors, and the Spiders of Metebelis 3.  She watched as the Docotr regenerated into his fourth incarnation.

Along with UNIT medical officer Surgeon-Lieutenant Harry Sullivan, she helped the Fourth Doctor against Professor Kettlewell's Giant Robot (which developed a fondness for fer); the Wirrn; another Sontaran named Styre; the Cybermen; and the Zygons.   She was there when Davros created the Daleks.  After Harry's departure, she continued her travels with the Fourth Doctor, helping him against the anti-matter monsters of Zeta Minor; Sutekh; the Kraals; Morbius; the Krynoids; the Mandragora Helix and Eldrad the Kastrian.  She announced she was fed up with traveling and wanted to leave the TARDIS, but when she heard that the Doctor had just been summoned to Gallifrey, she changed her mind and wanted to go with him.  However, the Doctor wouldn't take her and dropped her back in her own time (1977) and more or less her own space (in a place which was not South Croydon).

In 1981, Sarah Jane and a third version of K9, sent to her by the Doctor, defeated a coven of witches who worshipped the pagan goddess Hecate in Moreton Harwood.  Later that year, Sarah Jane was kidnapped by Borusa to take part in the Game of Rassilon.  She teamed up with the Third Doctor and, together with the Doctor's other incarnations and various companions, helped thwart the megalomaniacal Time Lord's plan for immortality.