Sarah Jane Smith
"Everything has its time, and everything ends."
Sarah Jane Smith - a journalist born in 1951 - used to travel with the third and fourth incarnations of the Doctor, but she was forced to leave the TARDIS when he was summoned back to Gallifrey. They were reunited years later whilst they were both investigating extra-terrestrial activity at a school.
Now, Sarah Jane has moved on and has started a new life for herself, fighting aliens and doing what she always did with the Doctor, but now with the help of her adopted son, Luke, and his friends, Clyde and Rani, however she is always on hand to help her old friend out at times of need.
The next time she saw the Doctor, it was to join in in the fight against Davros and his new Dalek race, and she saw him again briefly when he visited Bannerman Road just before his regeneration.