Franklin Delano Roosevelt ( DEL-ə-noh ROH-zə-velt, -⁠vəlt; January 30, 1882 – April 12, 1945), commonly known as FDR, was an American statesman and political leader who served as the 32nd president of the United States from 1933 until his death in 1945. He previously served as the 44th governor of New York from 1929 to 1933, the Assistant Secretary of the Navy from 1913 to 1920, and a member of the New York State Senate from 1911 to 1913.

Roosevelt attended Groton School, Harvard College, and Columbia Law School, going on to practice law in New York City. He won election to the New York State Senate in 1910 and then served as Assistant Secretary of the Navy under president Woodrow Wilson during World War I. Roosevelt was James M. Cox's running mate on the Democratic Party's ticket in the 1920 United States presidential election, but Cox was defeated by Republican Warren G. Harding. In 1921, Roosevelt contracted a paralytic illness that permanently paralyzed his legs. He returned to public office by winning the 1928 New York gubernatorial election. He served as governor of New York from 1929 to 1933, promoting programs to combat the Great Depression besetting the United States at the time. In the 1932 presidential election, Roosevelt defeated Republican incumbent president Herbert Hoover in a landslide.

During his first 100 days as president, Roosevelt spearheaded unprecedented federal legislation and issued a profusion of executive orders that instituted the New Deal. He created numerous programs to provide relief to the unemployed and farmers while seeking economic recovery with the National Recovery Administration and other programs. He also instituted major regulatory reforms related to finance, communications, and labor, and presided over the end of Prohibition. In 1936, Roosevelt won a landslide reelection with the economy having improved rapidly from 1933, but the economy relapsed into a deep recession in 1937 and 1938. Later, Roosevelt unsuccessfully sought passage of the Judicial Procedures Reform Bill of 1937. The conservative coalition formed in 1937 to block the implementation of further New Deal programs and reforms. He ran successfully for reelection in 1940, becoming the only American president to serve for more than two terms.

With World War II looming after 1938 in addition to the Japanese invasion of China and the aggression of Nazi Germany, Roosevelt gave strong diplomatic and financial support to China as well as the United Kingdom and the Soviet Union while the United States remained officially neutral. Following the Japanese attack on Pearl Harbor on December 7, 1941, he obtained a declaration of war on Japan the next day, and a few days later, on Germany and Italy. He worked closely with other national leaders in leading the Allies against the Axis powers. Roosevelt supervised the mobilization of the American economy to support the war effort and implemented a Europe first strategy. He also initiated the development of the world's first atomic bomb and worked with the other Allied leaders to lay the groundwork for the United Nations and other post-war institutions. He won reelection in 1944 but with his physical health seriously and steadily declining during the war years, he died in 1945. Since his death, several of Roosevelt's actions have come under substantial criticism. Nonetheless, historical rankings consistently rank Roosevelt as one of the greatest presidents in American history.