FDR was the first and only president to serve more than two terms. Passed by Congress in 1947, and ratified by the states on February 27, 1951, the Twenty-Second Amendment limits an elected president to two terms in office, a total of eight years.
Currently, only 15 legislatures in the United States have term limits. The longest term limit being 16 years total in the House or the Senate, enacted by the Arkansas General Assembly, after the 2014 election.
Term limits curb the potential of a political monopoly and prevent stagnation. Typically, the longer a politician is distanced from the life of their incumbents, the less likely they are to appropriately represent the current state of affairs.