Abstract Machiavelli creates his model of an ideal prince in his famous book The Prince. He abandons the Christian criteria set for a prince, such as generosity, morality, and piety. Instead, he claims that it is harmful for a prince to follow all the moral principles, and it is necessary for a prince to be well versed in the use of evil and treachery. Machiavelli¡¦s contemporaries, including the Tudors, are shocked by his vision of a prince unfettered by the constraints of traditional morality. Most of the Tudors regard his doctrines as atheism and immorality. Only some accept certain parts of his doctrines. This thesis intends to explore how Shakespeare deals with Machiavellianism in his two tetralogies. Does Shakespeare agree with Machiavelli in the definition of an ideal prince? How does Shakespeare think of the pragmatism Machiavelli advocates? Among the kings Shakespeare portrays in his two tetralogies, I choose King Richard III and Henry IV for my discussion, for these two kings correspond to the kinds of princes whom Machiavelli wants to offer advice to in his treaty, i.e., the new princes, or the princes who gain power recently. It is interesting that although both Richard III and Henry IV are usurpers and they both adopt Machiavellian statecraft, the way Shakespeare presents them proves very different. When portraying Richard III, Shakespeare follows the convention of the hero villain and makes him a stage Machiavelli. When portraying Bolingbroke, later Henry IV, he presents him as a man who revolts against the tyranny of his king, and a man who wins the crown with calmness, intelligence, and justice. Whenever Richard makes use of evil, he arouses detest and horror. When Henry adopts evil, it turns out to be necessary evil. However, the accounts and evidence recently found about Richard show us that the king, unlike what Shakespeare portrays, is not a hunchback, nor is he a murderous monster. On the contrary, he is a ruler of efficiency and responsibility. In my opinion, the reason why Shakespeare distorts Richard is that he intentionally portrays a king who fully demonstrates the dangerous teachings of Machiavelli in order to warn his contemporaries against the danger of accepting Machiavellianism. Obviously, he still cannot appreciate pragmatism and realism advocated by Machiavelli. Years after, when he composes the second tetralogy and writes about Henry IV, Shakespeare alters his attitude and comes to realize that it is not enough for a king to be good and virtuous; he has to be wise, active, resolute, and treacherous, if necessary¡Xto put it in another way: he has to be a Machiavellian prince. To sum up, as he grows older, a powerful and efficient monarch rather than a virtuous and pious prince becomes what Shakespeare longs for. We can say that Shakespeare matures in public affairs. Therefore, we see a Shakespeare crossing the boundaries of idealism and realism.