Vice President of the United States of America
The Vice President of the United States is the official who becomes President (or, in some cases, Acting President) in case of a vacancy in the presidency or the permanent or temporary disability of the President. Along with the President, the Vice President is elected every four years by the Electoral College or, if no candidate receives a majority of the electoral votes, by the U.S. Senate. The procedures for presidential succession are spelled out in the 25th Amendment to the Constitution.
The only official duty of the office is to preside over the U.S. Senate, with the authority to cast a tie-breaking vote. (In practice, though, the Vice President rarely attends Senate meetings, except on ceremonial occasions or when a tied vote is expected to occur. At most times, one or another member of the Senate actually wields the gavel.) Dick Cheney, a Vice President whose President had delegated significant responsibilities, only presided over the Senate on Tuesday afternoons.
Historically, the Vice President was the candidate for President who was the runner-up in the Presidential election, not the President's running mate.