4. Sarah Jane Smith
Sarah Jane Smith started off in the Pertwee era, and she was a very strong female character. A feminist journalist, she slipped into a research facility where the Doctor was staying, and she went by her Aunt's name, Lavinia. Of course, the Third Doctor didn't buy it at all, having read the research paper Lavinia wrote, and seeing how young Sarah was, he knew she wasn't Lavinia. But he played along with her for quite a bit, before having her admit who she really was. Sarah was definitely at her strongest in the Pertwee era, the writers wrote her extremely well. Take the episode Monster of Peladon for example, she puts her feminist side full force to help the queen. By the time she is with the Fourth Doctor, they start writing her poorly, slightly off character. She becomes more screamish, and depends more on the Doctor to get her out of trouble. Whereas in the Pertwee era, she was exploring on her own, managed to get out of minor things on her own. Basically she didn't have to always rely on the Doctor as she would later on. I loved her with Pertwee's Doctor. If they kept writing her as her character should have been all the time, she would have been perfect. I love Sarah, there were just some writing issues mixed with her character. Sarah Jane Smith is the only companion that has been a returning companion for multiple Doctors. She started with the Third Doctor, traveled with the Fourth Doctor, and ending her travels with him as well. She met the Fifth, First and Second Doctors in The Five Doctors, and also the Tenth Doctor. In the Sarah Jane Adventures, an episode called Death of the Doctor, Sarah meets Jo Grant, and together they meet the Eleventh Doctor. To see Sarah Jane and Jo Grant together was amazing, because it was the small reunion of the Third Doctor era of some sorts.