Answer:
Franklin D. Roosevelt was in office longer than any other American.
Explanation:
The 32nd President of the United States of America Franklin D Roosevelt served in office for a total of 4 terms. He is the only president to serve 4 Consecutive terms, in summary he served 12 years in office, Although U.S. Presidents are only allowed to serve 2 Terms during their presidency, pressing events such as the Great Depression and World War II allowed for him to extend his presidency.
Hope this helps,
H.M.