First of all, we need to define the meaning of the word "Machiavellian." Machiavelli was a famous—or infamous—Italian political theorist during the Renaissance. In his masterwork The Prince, he advocates the use of ruthless methods in acquiring and holding onto political power. Over the following centuries, the name of Machiavelli became a byword for cunning and treacherous behavior in the realm of high politics.

In Edward II, Mortimer Junior could reasonably be said to be Machiavellian in that he displays considerable ruthlessness in attaining and keeping power. At first, though, he seems to be animated by genuine grievances. Like many nobles of the realm, Mortimer has become thoroughly disillusioned with Edward's reign, which he sees as enervated by luxury and effeminacy. He's also none too happy at the refusal of Edward to pay a ransom for the safe return of Mortimer's uncle, Mortimer senior.

Initially, then, Mortimer Junior's opposition to Edward is based on principle. But the more powerful he gets, the less principled he becomes. Over time, he develops into a fully-fledged Machiavellian, having Edward murdered despite the king's willingness to vacate the throne without bloodshed. For good measure, he also manipulates his lover, Isabella—Edward's wife—and her son, the new king, in order to maintain his grip on power. In doing so, it's perfectly clear that Mortimer is displaying just the kind of amorality and ruthlessness that Machiavelli recommends to the Prince.