Sarah Jane Smith, occasionally rendered Sarah-Jane Smith, was an investigative journalist who travelled with the Doctor in his third and fourth incarnations. She held the honour of being one of the few people the Doctor considered one of his best friends. She reunited with him in his tenth incarnation and had adventures with him and his eleventh incarnation. Sarah met nine of the Doctor's incarnations in total: those already mentioned and the first, second, fifth, seventh, and eighth.
With the exception of K9, a robot dog gifted to her by the Doctor, Sarah spent most of her life alone after travelling with him, but maintained previous friendships with UNIT staff; her connections to the Doctor and the Brigadierafforded her enough pull with the group to call them in to mop up messes after a threat was averted.
In her later life, Sarah continued to repel any alien threats, while assisting more friendly ones. She eventually created a Xylok-based computer named Mr Smith to assist her by providing intel. These adventures lead her to take on her very own companions, forming a surrogate family; this group consisted of her adopted children of alien origins Luke and Sky, and her young neighbours, Maria, Clyde and Rani. Each had skills that helped Sarah in her adventures.