Josephine Grant is a fully-qualified UNIT agent, talented in such subjects as cryptology, safebreaking, explosives and escapology. Despite this, she still manages to be terribly clumsy.
It's not that Jo is stupid - she is, in fact, quite intelligent and independent. She is very good at analyzing the facts and coming up with a solution. But she can be rather overenthusiastic at times, taking actions that make the situation worse or just generally messing up. Fortunately, Jo manages to be completely endearing at the same time, so no-one can be angry with her for too long. She is an extremely good talker, and if the need arises, she can blabber on for minutes at a time without pausing. When the Doctor threatens to alienate people with his temper and blustering, Jo turns on the charm to smooth over the situation and obtain whatever the Doctor needs.
Jo was very keen to join up with UNIT, although the Brigadier was not as keen to have her, given her youth and inexperience. But, because she had relatives in high places, he allowed her to come on board, and with the Doctor griping over the loss of Liz, the Brigadier decided to assign Jo as his new assistant. The Doctor was less than thrilled, but could not find it in him to fire her, so Jo was kept on. Her friends apparently assume that life as an intelligence agent is swanky, full of good-looking James Bond types and suave dinner parties, when in fact most of Jo's time is spent with the Brigadier doing the filing at HQ, or running around making tea and being a general dogsbody.
Jo is not a scientist by training; although she did take general science at A-level, she didn't exactly pass it. She is pretty naive about all things scientific, and needs to have concepts explained to her, but the Doctor hopes to turn her into a scientist under his tutelage. She has had training in first aid, however, and usually carries a set of skeleton keys with her. She also seems to have some aptitude in repairing electronics and in martial arts, as well as being able to handle a gun, drive a hovercraft and ride a motorcycle. Eventually Jo also learns self-conditioning, which enables her to resist the Master's hypnosis techniques by reciting nursery rhymes.
But probably her feature that is most useful to the Doctor is her tendency to feel deep emotions. Jo is very much the sort who would immediately fall in love with a cute animal or child, and her sympathetic nature leads her to take up causes she believes in with great commitment. Once she has decided what needs to be done, she is stubbornly determined to do it. Jo cannot abide inaction - she is often to be heard saying "Well, we've got to do something!" Jo will pour her heart and soul into doing what she feels is right. In fact, she has even demonstrated on more than one occasion that she is willing to give her life to save the Doctor's.
Jo is a short girl with shoulder-length blonde hair and brown eyes, a ready smile and an infectious childlike laugh. She likes wearing high boots and lots of chunky rings. She gets on extremely well with the Doctor, and enjoys spending time with him, although she is often petrified by the monsters they encounter - the Drashigs, Mutants and Sea Devils are apparently the most frightening to her.
In the end, Jo found herself falling deeply in love with Professor Clifford Jones, an environmentalist who reminded her very much of a younger version of the Doctor. She agreed to marry him, and joined him on a trip to the Amazon rainforest in search of fungi to be used as meat alternatives. The Doctor gave her a sapphire from Metebelis 3 as a wedding present; she later returned it to him for safekeeping, as it was spooking the Amazonian natives.
