1. Ronald Reagan The country's oldest President, Reagan was 69 years, 349 days old when he was inaugurated, on Jan. 20, 1981. The former actor and governor was one of the most popular Presidents of the 20th Century. He survived an assassination attempt and championed tax cuts and defense spending, accelerating differences with the Soviet Union. During this same time, he and Soviet leader Mikhail Gorbachev negotiated a treaty to eliminate medium-range nuclear missiles. Reagan served two terms as President and was succeeded by his Vice-president, George Bush.