Martha Jones was a notable companion from the Russell T. Davies era for a number of reasons and one that was notable due to her role as a doctor herself and due to being the first woman of colour to be a full-time companion. She was fiercely intelligent, inquisitive and definitely one who wouldn't take a backseat, challenging the Doctor on any number of manners she thought fit. Her shining moment, perhaps, is in the third season finale which largely takes place during a dystopian Earth, one year after the Master's invasion - here she is a globe-trotting messianic preacher, telling the world about what the Doctor does and generally being a butt-kicking, relentless ace about the whole thing. Even during her capture, she's calm yet fuelled by rage - her family has been held captive and made the servants of the Master - and her speech to the Master which reveals that her and the Doctor's entire plan has been to backfire his own scheme with the power of belief. The Doctor is restored psychically and everything is put to rights. Martha gets her family back, time rewound, and a new career in UNIT and all. This doctor's not for turning.