Franklin Delano Roosevelt, the 32nd President of the United States, served the longest term in office with a record 4,422 days. He is the only president to be elected to four terms, though he died less than three months into his last term.
Franklin Roosevelt was first elected to the presidency in 1932 in the midst of the Depression. He was re-elected in 1936 and, in 1940, became the first U.S. president to be elected to a third term. The United States entered World War II the next year, and President Roosevelt went on to win an unprecedented fourth term in 1944. He died on April 12, 1945, and Harry Truman assumed the office of president.