Doctor Martha Jones played by Freema Agyeman
Matha Jones was on her way to the Royal Hope Hospital where she was a medical student when she first met the Doctor, although she didn't know it at the time. When she got to the hospital she met a new patient - Mr. John Smith.
Martha is very calm in a crisis, especially when the hospital is taken to the moon. The Doctor takes note of this and offers her a trip in the TARDIS. At first she doesn't believe he can travel in time - until he proves in by going back to when she was on her way to the hospital.
After facing the Master for a year that was eventually undone, Martha stays on Earth with her family. After a word from the Doctor she gets a job at UNIT, and turns up for a short period at Torchwood Cardiff.