Gerald Ford became Vice President and President of the United States without ever being elected to either position!
The Twenty-fifth Amendment to the United States Constitution deals with issues of succession to the Presidency and puts procedures in place for both filling a vacancy in the office of the Vice President, as well as responding to Presidential disabilities. The Twenty-fifth Amendment was adopted on the 23rd of February 1967. The Amendment has been invoked six times since its inception — twice with regards to Gerald Ford.
Spiro Agnew resigned on 10 October 1973, leaving the position of Vice President open. President Richard Nixon nominated Representative Gerald Ford of Michigan to succeed Agnew as Vice President, in accordance with the Twenty-fifth Amendment. The United States Senate voted 92 to 3 in favor of Ford and the House of Representatives voted 387 to 35 in favor. Ford was sworn in on 6 December 1973.
When President Richard Nixon resigned on 9 August 1974, after the Watergate scandal started unravelling, the Twenty-fifth Amendment had to be invoked again and Vice President Gerald Ford succeeded Nixon to the office of President. This resulted in Gerald Ford to be the only person ever in the history of the United States of America to be Vice President and President without being elected to either office by the citizens of that country.