1. Sarah Jane Smith
Played by: Elisabeth Sladen
First appearance: “The Time Warrior” (S11E01)
Companion to Doctors: Officially, Third, Fourth, and Tenth. She also met First, Third and Fifth in “The Five Doctors” and Eleven in The Sarah Jane Adventures.
Reason for departing: The Doctor was ordered back to Gallifrey and dropped Sarah Jane off on Earth, as humans were not allowed on the planet.
Sarah Jane Smith is considered THE quintessential companion by many. An investigative journalist who was suspicious of UNIT’s scientific advisor, Sarah Jane stowed away aboard the TARDIS and stayed there for several adventures, including the creation of the Daleks. She was present when the Third Doctor regenerated into the Fourth. She was smart and feisty and stood up to the Doctor. She went on to her own TV show, The Sarah Jane Adventures, where she continued to investigate alien activity on Earth with her son, Luke, and other curious kids. She is the companion who has known the most Doctors, and who has been his most consistent advocate and friend.