Martha Jones is a fictional female Human assistant in the Doctor Who series. The character was portrayed on screen by Freema Agyeman. Her allegiance / loyalty is to The Tenth Doctor. Martha becomes The Doctor's first non-white fellow traveller. She's a Doctor too, a Medical Doctor that is. Martha meets The Doctor when the Judoon borrow St. Thomas' Hospital and take it to the moon. Bored with medicine, Martha takes off with the Doctor.
We learn that Martha has a mother and a sister who both appear in the episodes. Martha is able to phone her mother after the Doctor has managed to connect her mobile up to the Tardis communication system. When Martha fears she is going to die in the episode 42, she calls her mum for help with questions to gain access to different parts of the ship.
Martha has a sister called Tish who appears in The Lazarus Experiment and the two part final episodes of David Tennant run as the Doctor. The Sound of Drums and Last of the Time Lords battling the return of Rassilon and the Master.
The last we see of Martha is when David Tennant's Doctor is about to regenerate, the Doctor visits a war zone where Martha is a soldier who has hooked up with Mickey, Rose Tyler's boyfriend. Still trying to work out how that happened, how they got together. It is revealed that they are married in the episode. The last time we heard from Mickey was when he went to the other dimension in the multiverse to stay with his blind gran.
Martha only stayed for one season before moving on for other things. Martha made a few appearances in the adult version of the series set in Cardiff known as Torchwood but that was only brief