In William Shakespeare’s tragedy King Lear, the fool functions in various ways, including the following:

• He “speaks truth to power.” In other words, he often tells Lear honestly what Lear needs to hear.
• He provides some comic relief in one of the darkest tragedies ever written.
• He riddles in ways that provoke Lear, the other characters, and the audience to think.
• He thus adds an element of mystery and inscrutability to the play.
• He is often a highly sympathetic figure, since he suffers along with Lear and partly because of Lear’s own foolishness.
• Despite his role as “fool,” he is actually one of the wisest characters in the play (certainly wiser than characters such as Goneril and Regan, who are cynically clever rather than truly wise).
• He is loyal to Lear when others desert the old king.
• He is a kind of counterpart to Edgar, who plays a different kind of “fool.”
• Like Cordelia, he loves Lear but refuses to flatter him.

The fool speaks in highly distinctive ways; his speeches are often hard to decipher, but sometimes he uses analogies that are reasonably straightforward, as in the following passage:

• Fool. Give me an egg, nuncle, and I'll give thee two 
  crowns.
• Lear. What two crowns shall they be?
• Fool. Why, after I have cut the egg i' th' middle and eat up the 
  meat, the two crowns of the egg. When thou clovest thy crown i' 
  th' middle and gav'st away both parts, thou bor'st thine ass on 
  thy back o'er the dirt. Thou hadst little wit in thy bald crown 
  when thou gav'st thy golden one away. If I speak like myself in 
  this, let him be whipp'd that first finds it so. 
  [Sings] Fools had ne'er less grace in a year, 
  For wise men are grown foppish; 
  They know not how their wits to wear, 
  Their manners are so apish.

Here the fool compares the two halves of an egg shell to Lear’s divided kingdom. He also compares his breaking of the egg into two parts to Lear’s division of the kingdom. Next the fool compares Lear to the old man who, proverbially, carried his own donkey on his back – a foolish thing to do. He then compares Lear’s bald head to Lear’s golden crown of kingship. Finally, he compares wise men to fools and to imitative monkeys. Here as so often elsewhere in his speeches, the fool’s analogies make him seem witty, clever, thoughtful, and thought-provoking.