Sarah Jane Smith
The Time Warrior-The Hand of Fear, K9 and Company, The Five Doctors, Dimensions in Time, School Reunion, The Stolen Earth, Journey's End, The Sarah Jane Adventures

Sarah Jane was a journalist from South Croydon, England when she entered the TARDIS while investigating the disappearance of scientists and technology by a Sontaran called Linx.  She returned to Earth when the Doctor was summoned to Gallifrey, but continued to combat alien threats to the planet with the help of K9.  In 2007 she reunited with the Doctor in his tenth incarnation and they investigated alien activity at Delfry Vale High School along with Rose Tyler and Mickey Smith.  Later on, Sarah Jane with her new neighbor Maria checked out the Bubbleshock factory where the popular beverage was manufactured, and they joined forces to continue the Doctor's work on Earth.