Willpower, Persistence, and to be Empathetic. These are essential. He needs a goal, plus an unconscious desire, usually the antithesis of what he thinks he wants. He cannot be passive. His goal, or desire, must be realistic so the reader can believe he might succeed, and the author must give him a chance to attain his goal. He must be likeable, though perhaps not always sympathetic. Some of the most wonderful heroes can be less than sympathetic, as in Dorothy Dunnett’s Francis Crawford. Yet the reader still empathises with him and his goals.
What reveals character? The choices he makes under pressure in pursuit of his desire. Choices made when nothing is at risk don’t amount to much. Does he tell the truth when a lie would save him? If he does, then we know he’s honest. Maybe stupid, but honest.
Writing experts say that a good, complex and truthfully written character should be revealed in the story as something more than he presents to the world. Easiest example: James Bond as rich playboy, but spy extraordinaire when the chips are down.
Most stories concentrate on the hero when he is initially thwarted in something. (If everything falls at his feet, there is no conflict, and thus no story. Give him a problem, watch him struggle with it.) What if he doesn’t succeed? What are the risks? What’s at stake? The bigger the stakes, the higher the risk, the better the story.