Sarah Jane Smith

Sarah Jane Smith was a young journalist who first met the Doctor while she was impersonating her aunt, Lavinia Smith (who was a famous virologist). She wanted to gain access to the top secret scientific base. She did not like the Doctor at first because she thought that he was the cause of several scientists going missing. She stowed away in the Tardis and she was transported back to medieval England in the first of her adventures with the Doctor. Sarah saw the Doctor regenerate for the fourth time, and she stayed with the Doctor, accompanied by Harry Sullivan Sarah stayed with the Doctor for a long time and she had to leave him when the Doctor was summoned to Gallifrey, so Sarah has to return to Earth. Sarah never forgot the Doctor, and the Doctor sent her a gift K9 Mark III. Sarah might have seen the Doctor again, if she had listened to K9, but she became involved with all of the five Doctors and was reunited with the Doctor in his third body.       

Sarah Jane Smith was in The Time Warrior to The Hand of Fear, plus The Five Doctors and K9 and Company: A Girl's Best Friend.