Abraham Lincoln, who invented a hydraulic device for lifting ships over shoals, was the only US president ever granted a patent.

Franklin D. Roosevelt was the only US president elected four times.

George Washington is the only man whose birthday is a legal holiday in every state of the United States.

Gerald Ford was the only US president not to have been elected to either the presidency or the vice presidency.

Grover Cleveland is the only US president to have been married in the White House.

James Buchanan was the only US president never to be married.

Richard M. Nixon is the only US president to have resigned.

Woodrow Wilson was the only US president to earn a doctorate.