James Madison

The slight, studious Virginian called the father of the Constitution, and the author of its sharpest defenses. His Federalist 10 and 51 are the spine of American constitutional thought: the argument that a large republic can control the mischief of faction, and that ambition must be made to counteract ambition. He later wrote the Bill of Rights into existence. Fourth President, lifelong student of how power is divided and held.