Machiavelli was famous during and after his lifetime. I am sure that if you know something about him you would know that he wrote his so called magnum opus 'The Prince', which was a philosophical work on politics and philosophy. Considered by many as the pioneer of political science, his works paved the way for politics treated as facts and figures, in a scientific manner, rather than a philosophical one as had been the case for hundreds of years before him. Most notably is his lack of use of morality as the basis for political action and motivation, instead appealing to pragmatism and efficiency.

It has been a while since I've brushed up on Niccolo so my memory might be a be a shady here. During his lifetime Mach floated in and out of 'influential' positions advising X and Y - often Medici. He wrote The Prince to, depending on what you read, to gain favour with the new Medici dude by giving him the 'Walkthrough to Ruling' or to trick the guy into becoming such a terrible ruler that there would be some form of revolt. The former position is the more well-known and the latter is academic journal speculation and such. In fact towards the end of his career/lifetime Mach was not an influential figure and used to dress up in this apartment and pretend to be engaging with the great leaders and figures of the past.

The Prince however was to become far more (in)famous. As, MisterMomo mentioned before me, the lack of morality in the book was shocking enough to survive the test of time. Some of his other work is very dry military-political instructions/observations that reflect a step-towards an empirical/scientific approach to politics.

Sorry for rather poor post quality - I will try and remember some specifics but I am sure there is someone more up-to-scratch than me to answer your questions.