The youngest president of the United States was Theodore Roosevelt, who assumed the presidency at the age of 42, following the assassination of William McKinley in September 1901. Roosevelt's energetic personality and progressive policies marked a shift in American politics during his time in office. He was known for his leadership in trust-busting, conservation efforts, and the promotion of the Progressive Movement. Roosevelt's presidency also saw significant advancements in foreign policy, including the construction of the Panama Canal and the Roosevelt Corollary to the Monroe Doctrine, which expanded American influence in Latin America.