At first glance, most people today would likely be perplexed and disturbed at calling a mother who kills her children a hero. But this stems from the common modern vision of a hero as the embodiment of "good- (and by contrast the villain as the embodiment of "evil-). In ancient Greek mythology and literature, especially as delineated by Euripides' senior colleague, Sophocles in his Oedipus Tyrannos, a hero was an individual who possessed a firmness of purpose more intense and steadfast than that of ordinary people. The hero had his own ideal vision of what was right and never swerved from that vision. And in making that vision a reality, he routinely aided his friends and destroyed his enemies, in the process committing some acts that, in and of themselves, modern spectators might find brutal, pitiless, and mean-spirited. Thus, a hero was not necessarily always "good- in the modern sense of the word. Despite the despicable act of killing her own children, Medea fulfills the definition of a tragic hero in the Sophoclean sense.
Medea is presented from the start of the play in heroic terms. Her language and action, as well as the familiar frame in which they operate, mark her as a heroic character, one of those characters whose purpose was specific, whose defiance of threats and advice, whose refusal to betray their own ideal vision were the preoccupation of Sophoclean tragedy. Medea is presented to the audience in the unmistakable style and language of the Sophoclean hero, the determined resolve, expressed in uncompromising terms: "the deed must be done- (791), and "I must dare- (1051), using the phrase "I shall kill- over and over again. The firmness of her resolve is phrased in the terms "my mind is made up- (1236, 822). She is deaf to persuasion. She is moved by the typical heroic passion, anger (176), wrath (94). As in Sophoclean heroic tragedy, there is also a secondary figure whose pliability under pressure throws the hero's unbending will into high relief.