Who was machiavelli and why was he significant in the florentine republic?

Niccolo Machiavelli was an official in the Florentine Republic from 1498 - 1512, during the years between the reign of the religious reformer Savanarola and the return of the Medici family to power in Florence.  He carried out various diplomatic missions for Florence during those years and had responsibility for Florence's militia.  But perhaps Machiavelli is most significant for his political writings, The Prince and Discourses on Livy.

Lorenzo de'Medici had ruled Florence for decades in a way that was popular. After Lorenzo's death in 1492, Dominican preacher Savonarola ran the city as a religious regime. Machiavelli's service in government occurred after Savonarola fell from power and was executed, and Florence operated very much as a republic.  When the Medici family again seized power in Florence in 1512, Machiavelli lost his government post.  He also was accused of conspiracy (a false charge). He was imprisoned and tortured, but after a few weeks was released.  In exile from Florence, Machiavelli wrote The Prince as a way of praising the style of rule of princes like the Medici, in hopes of gaining favor with the new rulers of Florence.  That didn't work, but The Prince has become a famous treatise in the field of political science. Machiavelli also wrote a lengthier work that extolled the virtues of a republic (closer to his own true views), Discourses on Livy.