Harry is a lieutenant in the navy and a surgeon by trade. He is a typically English sort of fellow, hailing from London, with a love for cricket and a relaxed demeanor. While working in the sickbay of UNIT, the newly-regenerated fourth Doctor was placed in his charge. While attempting to humor the Doctor's absurd belief that he could travel in space and time, Harry ended up getting swept away in the TARDIS on a "trip to the moon". But rather than a quick spin to the moon and back, Harry found himself being taken on a mad dash through time and space, and was very relieved when he finally got back to Earth!
Harry is extremely generous and full of concern for others, probably as a result of his medical training. He has a wonderful bedside manner, putting people at ease and showing them that he cares. Harry is not a very well-rounded person, though, and often feels out of his element during his travels with the Doctor. Even his medical talents usually do not help him, as the afflictions he sees are nothing like anything he knew on Earth. Because of this, Harry often finds himself floundering for something useful to do. Fortunately, he is a good fighter, although he seems reluctant to do so very often. He seems to be comfortable handling a gun, although his skills at actually firing one might not be as impressive.
His luck also tends to run badly. Although he may have the best of intentions, he often does the wrong thing. The Doctor once loudly proclaimed "Harry Sullivan is an imbecile!" but this is not a fair judgment. Harry is actually quite intelligent and capable, as long as he is comfortable with what he's doing. In fact, he can be downright clear-headed in a crisis, doing exactly the right thing and coming up with clever ideas.
Harry can be somewhat old-fashioned. His reaction to most surprises is "Oh, I say!" Sarah gets quite fed up with his slightly chauvinistic attitude and his insistence on calling her "old girl" or "old thing". Harry has brown hair and hazel eyes; he usually wears his naval uniform, blue jacket and trousers with a cravat and sometimes a hat, although he does sometimes get the opportunity to change into something different.
After Harry parted company with the Doctor and Sarah, he did run into them once again when he helped to foil the Kraal's attempted invasion of Earth. He later left UNIT for a top-secret job with NATO.
