Sladen joined Doctor Who in the 1973 serial, "The Time Warrior," as the new companion of the Third Doctor, played by John Pertwee. She stayed in that role for three years, tagging along as the Third Doctor became the Fourth (Tom Baker). So beloved by fans - and producers - of Doctor Who, she returned to the franchise numerous times: first in the 1981 spin-off "pilot," K-9 & Company, and then in the same year's anniversary special, The Five Doctors. In 2006, she returned to the revived series in the acclaimed "School Reunion" episode, which led to the BBC green lighting her own show, The Sarah Jane Adventures. She was shooting the fifth season of that series when she passed away.
I'm pretty sure that the first full episode of Doctor Who I ever saw was "Robot," on PBS back when I was in art school, around 1983 or 84. Sladen co-starred with Tom Baker in that story, and I think I fell in love with her right then and there. Sarah Jane Smith is still my favorite Doctor Who "companion," and proved herself a formidable heroine in her own right. Smart, brave, cute-as-a-button and prickly as a cactus, Sarah Jane - and by extension, the actress who portrayed her so well - was my kind of woman.
Rest in Peace, Ms. Sladen... and so long, Sarah Jane - the finest companion a time traveler could ever hope for.