Shakespearian play King Lear presents a very interesting character that is called just as "the fool".
Going back in time it's possible to find the presence of this singular person in the Middle Ages, when the fool was responsible for entertaining the kings and the nobles of the kingdom. Contradicting the real meaning of his title, the fool was not exactly a fool or mad person, actually he used to be very smart. According to Asimov (1970), if the "poor fellow" just pretended to be mad but had a clear vision of facts and was "pungently clever" it was enough to be a good fool.
That's exactly what happens in King Lear. At first the audience may think that the fool is a simple character who's there to make them laugh throughout the play, behaving as if he had no sanity. As long as the facts are developed, however, the fool shows himself as a clever person, actually one of the few people who really see things the way they really are. Of course his function is to entertain the king - and the audience, as well -, but every joke he says to the king is full of sarcasm, as if he knew more than the king himself, although he really did, this is a kind of wit humor.
Sometimes the fool even wants to show the king that he has committed a huge mistake dividing his kingdom the way he did, it is said by the fool in a quite offensive way, although the king doesn't give importance to his joker. We can see it in the first act of the play, when Gonerill enters:.
Thou wast a pretty fellow when thou hadst no need to care for her frowning; now thou art an O without a figure. I am better than thou art now. I am a fool, thou art nothing. (I; 4; 150 - 152).