The President of the United States of America is the head of state and head of government of the United States. The office of president was established upon the ratification of the United States Constitution in 1788 and the first president took office in 1789. The president serves as the chief executive and leader of the executive branch of the United States government. Article Two of the United States Constitution establishes the president as the Commander-in-Chief of the armed forces and enumerates powers specifically granted to the president, including the power to sign into law bills passed by both houses of the Legislature, to create a Cabinet of advisors, to grant pardons or reprieves, and, with the "advice and consent" of the United States Senate, to make treaties and appoint federal officers, ambassadors, and federal judges (including Justices of the Supreme Court of the United States). Article Two also defines a presidential term at four years; subsequently, the Twelfth Amendment (1804) revised the procedure for electing the president and the Twenty-second Amendment (1951) established presidential term limits. The United States was the first nation to create the office of president as the head of state in a modern Republic, and today the presidential system of government is used in many countries throughout the world. As of 2007, forty-two men have been Presidents of the United States.