Niccolò Machiavelli: (1469-1527) Italian political philosopher and bureaucrat.
Machiavelli, who worked much of his life as a top bureaucrat in his native city Florence, was the first to consciously try to reason about power in society in a realistic manner, not based on what people, politicians, princes and powerholders wish to believe or pretend to believe, but based on what they really do.
His most famous book is The Prince (Il principe), but The Discourses (Discorsi sopra la prima deca di Tito Lavio) gives a more true, more complete, and more realistic statement of his opinions.
He also wrote for the stage, and wrote a fine History of Florence.
The best later statement of his ideas is probably by Gaetano Mosca's The Ruling Class (Elementi di Scienza Politica). There is an interesting booklet by Burnham, The Machiavellians, that summarizes the ideas of some political philosophers influenced by Machiavelli.