Her death is a huge loss to
Doctor Who fans, and to fans of strong female adventure heroes everywhere. It's hard to overstate how important Elisabeth Sladen was to
Doctor Who, and how much she transformed the role of the companion on the show. In many ways, she paved the way for all of the show's more intelligent, resourceful companions in the 21st Century.
When her character, Sarah Jane Smith, was added to the show in 1973, she was a direct reaction against the ditzy, spacey Jo Grant, her predecessor. And at first, Sarah Jane Smith was conceived of as a sort of plucky girl reporter, like Lois Lane, who would spout lines about "Women's Lib" every now and then. In her very first scene, Sarah Jane has a stereotypical 1970s feminist moment with the Doctor, who asks her to make herself useful by making coffee. Later, Sarah Jane gives the struggling Queen Thalira a crash course in standing up for herself. Watching those early episodes, you sense that the show is cluelessly trying too hard to make Sarah Jane a strong female character.
And by the time Tom Baker took over as the Doctor, Sarah Jane was being pushed into the traditional "damsel in distress" role more often. She spends a lot of Baker's first year squealing, screaming, being pushed off cliffs, getting sick and being trapped in impossible situations that the Doctor and Harry have to get her out of. Sladen has mentioned several times that she complained to the producers about this state of affairs, and seriously considered leaving the show after her second year.

Instead, the character of Sarah Jane changed, and became what the producers had originally struggled to make her: a strong, independent woman. In Baker's second season, Sarah Jane figures stuff out as often as the Doctor does, and frequently stands up for herself. On the DVD of "Pyramids of Mars," director Paddy Russell (one of the show's few female directors) explains how she and Sladen reworked the scripts, giving some of the Doctor's lines to Sarah Jane — so instead of the Doctor explaining stuff to Sarah Jane, it became Sarah Jane working things out on her own.

In those later stories, Sarah Jane is more of an equal partner to the Doctor, and often plays a crucial role in defeating the alien menace. And she gets one of my favorite companion moments in "The Seeds of Doom," when the thuggish Scorby laments that all his armed guards have fled the scene of the Krynoid attack, "just like a bunch of women." A few moments later, Sarah Jane is preparing to go face the Krynoid alone, and Scorby tells her it's suicide with that creature roaming around. She turns to him and says, "What was that you were saying about women?" The look on her face is priceless.
Sarah Jane was one of the longest-lasting
Who companions, appearing for three and a half seasons. And unlike most companions, she continued to have an impact on the show long after her depature.
When Baker himself was planning on leaving
Doctor Who, then-producer John Nathan-Turner asked Sladen to come back as Sarah Jane Smith for a while, to help ease the transition between Doctors. Sladen turned down that idea, but agreed instead to star in a spin-off series called
K-9 and Company, in which she teamed up with the Doctor's robot dog to solve mysteries. Sadly,
K-9 and Company was not that great a show, and it was soon forgotten, except that Sarah Jane and K-9 both put in repeat appearances in the 1983 special "The Five Doctors."
And somehow, the character of Sarah Jane never went away. Sladen reprised the role in 1990s audio adventures with Jon Pertwee as the Doctor, "The Paradise of Death" and "The Ghosts of N-Space." (Memorably, in one of them, she explains Sarah Jane's first law of journalism: Always make sure your expenses are taken care of.) She also starred in a series of nine Sarah Jane audio plays, including "Comeback," "The Tao Connection," "Test of Nerve," "Ghost Town," and "Buried Secrets," for Big Finish Productions in the early 2000s.