Evil - Tyrants

"Remember that is is not by a tyrant's words, but only by his deeds that we can know him."

-Dwight David Eisenhower

Immediately when I saw this quote I thought of Macbeth. Macbeth seems to have high respect for Duncan, which he does. However, his ambitions to take the throne after hearing his prophecy that he becomes corrupt and his sincere words become meaningless after he kills gracious Duncan. He becomes a tyrant once he gets the throne because he kills Banquo in his paranoia. Many other murders follow once Macbeth inherits the crown of Scotland. Macbeth's show his true colors and that any man can become a corrupt tyrant when given power.

EEEEEEEVIL!

Evil: morally reprehensible; sinful, wicked; arising from actual or imputed bad character or conduct.

Well, up to this point we have read of some interesting events going on in Macbeth. Evil has been a prominant theme.

In what ways have we seen evil up through Act III? How has it affected the plot?
What makes a person evil?