|A young Elisabeth Sladen with K-9|
As a result of her appearance along with K-9 in that David Tennent story School Reunion she was given what was her second spin off series The Sarah Jane Adventures having previously been in the short-lived K-9 and Company in the 80s.
The new generation of Doctor Who fans including my nephews will always have as their first companion Rose Tyler as played by Billie Piper. For people of my vintage the first companion we remember is Sarah Jane. So her return to the new series was like us revisiting our childhood. Indeed when she left the series in 1976 serial The Hand of Fear it was the first time that the leaving of a companion caused as much media interest as the previous three Doctors leaving.
She first appeared as an investigative reporter when the Doctor himself was undercover to the Smith and Jones was born, the Doctor used in the pseudonym Jones when he needs to have a last name. But she also was the first of the companions to actually have a strong personality and really be able to get some solutions even before the Doctor managed which is why she stands out as a iconic assistant. She will be sadly missed amongst the Whovians from here to the co-ordinates of Gallifrey, although I suspect some lifeforms within metal containers may well CEL-LE-BRATE. However, I'm sure if they do so in front of the Doctor his sonic screwdriver may well get revenge for us all.
Elisabeth Sladen 1948-2011