Franklin Delano Roosevelt (January 30, 1882 – April 12, 1945), the 32nd President of the United States, was a central figure in world events during the mid-20th century, leading the United States during a time of worldwide economic crisis and world war. The only American president elected to more than two terms, he was often referred to by his initials, FDR. Roosevelt won his first of four presidential elections in 1932, while the United States was in the depths of the Great Depression. FDR's combination of optimism and economic activism is often credited with keeping the country's economic crisis from developing into a political crisis. He led the United States through most of World War II, and died in office of a cerebral hemorrhage, shortly before the war ended.

Roosevelt's approach to the economic situation he inherited is known as the New Deal. The New Deal consisted both of executive orders and legislation pushed through Congress. Executive orders included the bank holiday declared when he first came to office; legislation created new government agencies, such as the Works Progress Administration and the National Recovery Administration, with the intent of creating new jobs for the unemployed. Other legislation provided direct assistance to individuals, such as the Social Security Act.

As World War II began in 1939, with Japanese occupation of countries on the western Pacific rim and the rise of Hitler in Germany, FDR kept the US on an ostensibly neutral course. Once war broke out in Europe, however, Roosevelt provided Lend-Lease aid to the countries fighting against Nazi Germany, with Great Britain the recipient of the most assistance. With the Japanese attack on Pearl Harbor on December 7, 1941, Roosevelt immediately asked for and received a declaration of war against Japan. Germany subsequently declared war on the United States on December 11, 1941. The nearly total mobilization of the US economy to support the war effort caused a rapid economic recovery.