Downfall: The downfall of Macbeth in William Shakespeare's play Macbeth begins when he listens to the three witches on the blasted heath, although we can also assume that there was some flaw in his character that made him listen, as Banquo was able to resist their blandishments. We see Macbeth, urged on by his wife decide to kill Duncan despite admitting that Duncan is a good king and that there is no moral justification for so doing in the passage:
I have no spur
To prick the sides of my intent, but only
Vaulting ambition, which o’erleaps itself
And falls on the other—
Act 1, Scene 7, Lines 25-28
Once Duncan has been killed, Macbeth descends into life as a brutal tyrant.
Tragic hero: A tragic hero is not necessarily a "good guy" in the sense of a hero in a movie. Instead, he (or she) is a figure of a certain grandeur or importance who makes a fatal mistake ("hamartia", literally a spear thrown that cannot be recalled once it has left the hand). Thus Macbeth as we see him at first is a skilled warrior and battle leader, honoured by Duncan, who decides to yield to his ambition and kill Duncan (the hamartia, or irrevocable act), an act that leads to his downfall.