A Shakespearean tragic hero, is one who is of noble birth; with qualities that the audience can identify with. He is basically a fine man and yet not so fine that he seems elevated beyond the reach and understanding of the people in the audience. His goodness and potential for greatness are marred by a single failing; and this failing is something that the average man in the audience might possess. Thus the members of the audience get caught up in the drama surrounding the tragic hero because they are able to identify with his dilemma. Because of this identification, the audience experiences feelings of pity (for the hero) and terror (because such a fate could have befallen them, after all). At the end of the play, when the hero dies, they experience a catharsis of these emotions - that is they are drained of these emotions.
The protagonist or hero of a Shakespearean comedy has not the same stature as the hero of a tragedy. He too is of noble birth but he is a slighter figure - and his potential for greatness is never tested.