Sarah Jane was one of the most iconic of the Doctor's companions. In proof of that she is the only one to have had TWO goes at a spin off series and is one of the few classic series characters to have returned in the new Doctor Who series. In 2007 she got her own series.

The Sarah Jane Adventures

Invasion of the Bane
Revenge of The Slitheen
Eye of the Gorgon
Warriors of Kudlak
Whatever Happened to Sarah Jane?
The Lost Boy