James Madison
James Madison was the primary author of the United States Constitution as well as the Bill of Rights that was added to it. He also served as the 4th President of the United States.
[edit] As author of the Constitution
As the Articles of Confederation began to crumble, Madison took it upon himself to draft a new constitution for the country (commonly known as the "Virginia Plan".) James Madison was by no means a novel political theorist, but in crafting the US Constitution he drew on a long legacy of such writings in Europe, notably John Locke and Montesquieu. It called for a separation of power and checks and balances, while still giving the federal government more centralism and more overall power.
In the end, the Virginia plan was not accepted wholesale, but was instead modified dramatically in order to win approval by all of the 13 states. Despite the modifications, James Madison still argued (along with Alexander Hamilton and John Jay) for the ratification by all of the states. Together, the three wrote the Federalist Papers to argue for a stronger government. (Sadly, after this Hamilton and Madison became strong political enemies, with Hamilton wanting a much stronger federal government than Madison was comfortable with.)
Originally, Madison was opposed to a separate "Bill of Rights," fearing it would be only a paper cover and would specifically make people think that rights not listed did not exist. However, it became clear that it would not be accepted without some kind of additional modifications, and so Madison wrote up some of the first explicit prohibitions for a government to be involved in matters of conscience. His original desire was for these to be applied to the states as well, but that had to wait until after the American Civil War.
[edit] President
Madison's presidency was mostly taken up with the rivalry (and then war) with Great Britain. The war saw some very dramatic losses for the United States, including the sacking of Washington, DC, but by the end the war was considered a clear draw. Many in the US saw it as a win, as it consolidated the status of the US as an independent nation.
A much more successful war was waged against the Barbary Pirates yet again, bringing an end to the habit of paying tribute to them.
Madison was the smallest president, only 5'4" and about 100 pounds.[1]