This biography of George Brinton McClellan Jr., son of the Civil War general, a congressman, and mayor of New York (1904–1910), studies political courage and honor. McClellan was a Tammany Hall Democrat, who challenged the boss of Tammany Hall, Charles Francis Murphy, and put principle above party. For his disloyalty, he paid the price of political oblivion. Today, this important figure in the modernization of the city is hardly remembered because of the power of his enemies. This study emphasizes McClellan's six years as mayor, but also covers his youth, relationship with his father, his career as a reporter, years as a congressman, and his post-political career, which included his tenure as an economics history professor at Princeton, his brief army career during World War I, his retirement years in Washington, D.C., and his burial in Arlington Cemetery.