Historians discuss the role of Henry Clay (1777-1852) in American politics. Known as the "Great Compromiser" but also as "The Dictator," he ran five unsuccessful presidential campaigns. Perhaps the most powerful politician of his time, he served as speaker of the House, U.S. senator, and secretary of state. This is the first of our 14-week series called "The Contenders: They Ran & Lost but Changed Political History."