Aristotle's discussion of tragedy in his Poetics has become the definitive work on this dramatic art. With regard to the characters in this art form, Aristotle describes them as noble personages, who are "better than ourselves"  and they perform noble actions. The protagonist, or tragic hero, is not perfect albeit noble in character. For, his misfortunes are a result of a deficiency in his nature which Aristotle terms hamartia. Hamartia is defined in Perrine's Literature: Structure, Sound, and Sense as

a criminal act committed in ignorance of some material fact or even for the sake of a greater good.

Thus, this act evokes a certain pity from the audience.  Often, too, the tragic hero has a discovery, or a change from ignorance to knowledge or both, in keeping with his noble nature. 

Because of the existence of the tragic hero's hamartia, it is important to note that the inherent nature of the tragic hero determines his qualities, and these qualities together with his thoughts drive his actions. So, in tragedy, events do not just follow one after another; rather, they follow because of one another, and character is, thus, subsidiary to the dramatic action of the tragedy. For instance, in Sophocles's famous play, Oedipus Rex, a standard of tragedy, the action of the play clearly follows because of his earlier act of slaying his father.