At first, Hamlet suggests that vengefulness in a corrupt court is a kind of sanity, when he vows to put on an antic disposition, but he acts in a way that is more and more contrary to his moral nature as the play goes on, rebuking his mother against the ghost's first injunction not to harm her and to leave her to her conscious, killing Polonius on an impulse after sparing Claudius at prayer, speaking harshly to Ophelia beyond what she deserved when he suspects he is being observed, and also claiming to her brother he loved Ophelia more than a brother. A loss of identity, vengeance and madness are linked in the stories of the other characters in "Hamlet" to a lesser degree. Even Claudius suggests that it was his ambition and his passion that moved him to fratricide, not 'himself' in his ineffectual prayer, and he blames his actions towards Hamlet on the need to avenge Polonius' death without offending Gertrude who "lives almost by his looks," and the Danish commoners who also love her son (IV.7). Laertes repents of his actions before death, and blames the king, not his own will for his vengeful actions towards Hamlet. Finally, it is suggested that the sight of his mad sister Ophelia moves Laertes to become an avenger, and to do things not characteristic of his true nature. Of course, the 'most legitimately' mad character in the play, Ophelia, does harm to herself, not to others, but she does spur on her brother's anger against Hamlet: "Hadst thou thy wits, and didst persuade revenge, / it could not move thus" (IV.5).

The association between madness and revenge in "Hamlet" suggests that both madness and the nature of vengeance displace the individual's true identity and spur him or her on to uncharacteristic actions. When Hamlet tries to...

This makes sense in the original plot of the tale -- Amleth is bound to revenge his father, and everyone in Feng's court is well aware of this, in contrast to that of the more modern Danish court setting of "Hamlet." By pretending to be "witless," Amleth keeps the evil Feng's suspicions in check. But by showing how taking on the new identity of an Elizabethan avenger is like throwing off one's old, moral identity, and thus like a kind of madness, Shakespeare reinterprets and adds more psychological complexity to the Amleth story, as well as complicates the question of how much Hamlet wants revenge, and how mad Hamlet is at various points of the play.
Works Cited

Best, Michael. "Amleth/Hamlet." Shakespeare's Life and Times. Internet Shakespeare

Editions, University of Victoria: Victoria, BC, 2001-2005. 21 Apr 2008. http://internetshakespeare.uvic.ca/Library/SLT/history/amleth.html

Pennington, Michael. Hamlet: A User's Guide. New York: Limelight Editions, 1996.

Shakespeare, William. "Hamlet." Shakespeare Homepage. 7 Apr 2008. http://shakespeare.mit.edu/hamlet/hamlet.1.5.html