Sarah Jane Smith is one of the most enduring figures in the Doctor Who universe, appearing as a regular companion to two incarnations of the Doctor (Jon Pertee's third Doctor and Tom Baker's fourth Doctor) between 1973 and '76 and occasionally popping up ever since. The character currently has her own spin-off show, The Sarah Jane Adventures that is nominally intended for children. BBC America has just released the first season of The Sarah Jane Adventures on DVD (look for Science Not Fiction's review tomorrow), and so I got to talk to the woman behind Sarah Jane, actress Elisabeth Sladen, about playing such a popular character and other things Who. Science Not Fiction: How has the character of Sarah Jane changed between 1973 and 2008? Elisabeth Sladen: Dear me -- you know, I once called her a cardboard cut out! But that’s what was on the page [of the script] when it was presented to me. It just said, "Enter Sarah Jane." If you’re used to plays, [those scripts] say "Enter Mary Jane. She’s 5’4” tall. She has a limp. She doesn’t like her father," -- you’re clothed. I just looked at this script and I thought "Oh my god, what the hell am I going to do with 'Enter Sarah Jane?'" Well, I love Doctor Who. I had two Doctors, and I was able to progress a little bit with their input, because you react off them. When I left [in 1976] I thought, "How lovely. [But] that's the end of that." Then what happened was I never stopped getting letters. And you lovely Americans, you kept it alive for me as well, I would go over there and talk about it ... answering questions, would she do this, why did she do that, why wouldn't she do this. Then [in the '80s] the BBC got the videos out [and] you had a new audience. I'd start to get questions as the years went on: where do you think she would be now, what would she be doing, so in my brain I'd be adding to her, she was growing all that time. I used to say "[Sarah Jane] is nothing like me, I just played this character," but I as you go on over so many years with something you add yourself to it. So by the time Sarah Jane got to School Reunion [a 2006 episode of Doctor Who, where Sladen reprised her role alongside David Tennant's tenth Doctor] you know there was a lot more going on. It was a brilliant script by Toby Whithouse, so where I thought she would be. It was just seamless for me. I do think I add more of myself now, [for example] being in The Sarah Jane Adventures a surrogate mum, you know I am a mum, so that kind of comes quite well. SNF: Why do you think the the character of Sarah Jane Smith has such longevity? ES: I hesitate to answer, because I think it’ll jinx it! I just am so thankful for it because the fans have been so good to me.