Sarah

Sarah first appears in the Third Doctor serial The Time Warrior, where she has managed to infiltrate a top secret research facility by posing as her aunt, Lavinia Smith, a famous virologist. Sneaking into the TARDIS while the Doctor is preparing to follow the trail of a kidnapped scientist through time, she becomes embroiled in the subsequent adventure in the Middle Ages.

Sarah then finds herself working with the Third Doctor and UNIT on a number of occasions. She is present when he regenerates into the Fourth Doctor at the end of Planet of the Spiders, and continues to accompany him on his journeys through time and space.

As a companion she is confident and inquisitive, and possesses a sharp mind as well as a sharp tongue. She is also a feminist — in her first appearance she is infuriated when the Doctor asks her to make coffee, and she often verbally spars with fellow companion Harry Sullivan, who has an old-fashioned and unintentionally patronising attitude towards her. However, this does not get in the way of forming a close friendship with him. In The Monster of Peladon, the Doctor advises Sarah to share concepts of Women's Lib with Queen Thalira, whose power is limited on her planet because of her gender. In later episodes, Sarah's views become less vocalised, but she never gives the impression that she is less than capable. In spite of the dangerous and frightening situations she often finds herself in, she loves adventure and risk, and in spite of her outward complaints, is always thrilled to go off in search of more adventure. She shares a rapport with the Third and Fourth Doctors, and is consistently one of the Doctor's most popular companions among fans.

The exact placement of Sarah's adventures with the Doctor is part of the UNIT dating controversy. In Pyramids of Mars she states (more than once) that she was "from 1980", which implies that her adventures with the Doctor took place in the near future with respect to the time of broadcast. However, fans continue to argue whether she means 1980 as the year she came from, the year she last returned to Earth, or the year she believes it is in her personal chronology.

During her time with the Doctor, Sarah encounters Daleks, Cybermen, antimatter creatures on the most distant planet in the universe, android mummies in 1911 England, ancient evils in 15th century Italy and other dangers, until she is returned to Earth at the end of The Hand of Fear.

Her decision to leave the TARDIS and return home coincides with the Doctor's summons to his home planet, Gallifrey, to which he was forbidden to take humans at that point. However, his attempt to materialise the TARDIS near her flat in South Croydon falls short of the mark. Thirty years later, when she encounters the Tenth Doctor in "School Reunion", she reveals that he had in fact abandoned her in Aberdeen, Scotland. Between being dropped off by the Fourth Doctor and meeting the Tenth Doctor, Sarah was herself summoned to Gallifrey where she was reunited with the Third Doctor, and met the First, Second and Fifth Doctors (in The Five Doctors). In the period after she was returned to Earth, she tells the Tenth Doctor, she gave up waiting for him to return and concluded that he had died on whatever mission he had been sent.

At the time of "School Reunion"', Sarah is still single, and suggests to the Doctor that she found it difficult to hold down a lasting relationship with any man following her experiences with him. At the episode's conclusion, he leaves her a new K-9 model, to replace the destroyed K-9 Mark III he sent her as a gift prior to the events of The Five Doctors.

In the lead-up to the broadcast of "School Reunion", Sladen was quoted in The Daily Mirror being somewhat critical of the characterisation of Sarah Jane in the original programme: "Sarah Jane used to be a bit of a cardboard cut-out. Each week it used to be, 'Yes Doctor, no Doctor', and you had to flesh your character out in your mind — because if you didn't, no one else would." She spoke more favourably of the characterisation in the new series.