Harry is rather old-fashioned and stereotypically English in his attitudes. Somewhat accident-prone, he once claimed he was always trapping his nose in the doors of Portsmouth barracks. He often employs slightly archaic language — for example, referring to Sarah Jane affectionately as "old thing" or "old girl". He is nonetheless depicted as possessing great bravery and a "can-do" attitude, adapting well to the many strange situations in which he finds himself. He can, however, also be quite clumsy and unsubtle, once leading the Doctor to declare, in a moment of frustration and at the top of his lungs, that "Harry Sullivan is an imbecile!" Nonetheless he is well liked by the Doctor and Sarah Jane, and has a slightly flirtatious relationship with her.