Final answer:
A hero's downfall in literature is often caused by a weakness or defect known as 'hamartia', which is typically a tragic flaw like excessive pride or hubris. Famous examples include Creon's pride in 'Antigone' and Oedipus's arrogance in 'Oedipus Rex'.
Step-by-step explanation:
The weakness or defect that can lead to a hero's downfall in a tragedy is called hamartia. Often a piece of their character that is otherwise noble or a great strength, this tragic flaw becomes their undoing. For instance, the character of Creon in Antigone exhibits hubris, or excessive pride, which ultimately leads to his downfall.
Similarly, the Greek hero Oedipus is renowned for his intelligence, but it is his arrogance, a form of hubris, that triggers his tragic end. Importantly, the concept of the tragic hero, as defined by Aristotle in his Poetics, includes characteristics such as goodness and nobility alongside the fatal flaw, leading to a dramatic storyline filled with peripeteia, anagnorisis, and finally resulting in catharsis for the audience.