Who was the only American elected 4 times to the highest office of the president?

Franklin Delano Roosevelt 1933-1945. He was succeeded by Harry S.Truman Roosevelt died of a cerebral hemorrhage in Warm Springs, GA on April 12, 1945. This explains the 13 as opposed to 16 years he should have served. Thus leaving the rest of his term to Harry S. Truman his Vice-President.