Using only four adjectives, summarize the character of Macbeth in Shakespeare's Macbeth.

The adjectives I would use here are
ambitious, obsequious,
paranoid and evil.  The most
important adjective here is most certainly the first one!  Why?  Because it is Macbeth's
ambition that makes him one of Shakespeare's most notable tragic heroes.  Macbeth admits
this himself when he says:

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I have no spur /  To prick the sides of my
intent, but only / Vaulting ambition, which o'erleaps itself / And falls on th'
other--

It is this ambition,
in addition to his mindless following of his wife's advice that cause him to murder. 
This leads me to the second adjective: obsequious.  Macbeth does nothing if he doesn't
follow his wife's lead.  In fact, many critics think that Lady Macbeth is the true
genius behind Macbeth's evil!  What is the first thing Macbeth does when he hears about
the prediction? Writes his wife a letter to see what she thinks!  She then
says,

Come,
you spirits / That tend on mortal thoughts, unsex me here, / And fill me, from the crown
to the toe, top-full / Of direst
cruelty?"

Why?  To convince
her husband! ... And she does a heck of a good job, too!  Little Macbeth follows along,
not unlike a little puppy dog and lets his evil wife lead him forth into
evil.

Now to deal with the fact that Macbeth is paranoid. 
It is the evil in the witches' predictions that make him thus!  Everything from finding
the ghost of Banquo sitting at the banquet, ... to Macbeth's own order of murder.  And
can there be anything more indicative of paranoia than looking around frantically for
walking trees?  Of course, he's worried about those Birnam Woods coming to Dunsinane. 
In my own opinion, I think that Macbeth is more paranoid about the witches' predictions
coming true than he is protective of his own
kingship.

Finally, we can't neglect the fact that Macbeth
is evil, ... or perhaps I should say that he turns evil in the
context of the play.  Thanks a lot, Lady Macbeth!  Simple ambition turns sour when that
ambition turns to murder.  Macbeth murders on his own, ... and he hires others to murder
for him.  There is no doubt that an evil person only would commit this type of crime to
raise his own station!  No wonder the witches spend lots of time laughing at
Macbeth!