The main duty of the Vice President of the United States is to act as the presiding officer of the Senate. The Vice President also serves as part of the President's administration and as a ceremonial assistant. The Vice President holds the second highest office in the government and must be ready to take on the role of President if something happens to the President.
The Vice President is part of the Executive Branch of the United States government. He takes over for the President if the President dies, resigns, is incapacitated, or if he is deemed by the Cabinet as unable to perform Presidential duties.
The Vice President casts tie-breaking votes on behalf of the President in the Senate. More often, though, the Senate elects a new Senate member each day to take on this role. Duties of the Vice President outside of what is listed in the Constitution are directed by the President.
As of 2015, fourteen former Vice Presidents have become President: some took over office after the President died, some ran for office after their Vice President term, one was a fugitive after he murdered a man, and one left office to join the Confederate Army. Seven Vice Presidents died while they held office, and three were Nobel Peace Prize recipients.