The president of the United States is the head of state and head of government of the United States, indirectly elected to a four-year term by the people through the Electoral College. The officeholder leads the executive branch of the federal government and is the commander-in-chief of the United States Armed Forces.

Since the office was established in 1789, 44 men have served as president. The first, George Washington, won a unanimous vote of the Electoral College. Grover Cleveland served two non-consecutive terms in office (the only president to have done so) and is therefore counted as the 22nd and 24th president of the United States; the 45th and current president is Donald Trump (since January 20, 2017). There are currently four living former presidents. The most recent former president to die was George H. W. Bush, on November 30, 2018.

The presidency of William Henry Harrison, who died 31 days after taking office in 1841, was the shortest in American history. Franklin D. Roosevelt served the longest, over twelve years, before dying early in his fourth term in 1945. He is the only U.S. president to have served more than two terms. Since the ratification of the Twenty-second Amendment to the United States Constitution in 1951, no person may be elected president more than twice and no one who has served more than two years of a term to which someone else was elected may be elected more than once.^[17]

Of those who have served as the nation's president, four died in office of natural causes (William Henry Harrison, Zachary Taylor, Warren G. Harding, and Franklin D. Roosevelt), four were assassinated (Abraham Lincoln, James A. Garfield, William McKinley and John F. Kennedy), and one resigned (Richard Nixon, facing impeachment). John Tyler was the first vice president to assume the presidency during a presidential term, and set the precedent that a vice president who does so becomes the fully functioning president with his own presidency, as opposed to a caretaker president. The Twenty-fifth Amendment to the Constitution put Tyler's precedent into law in 1967. It also established a mechanism by which an intra-term vacancy in the vice presidency could be filled. Richard Nixon was the first president to fill a vacancy under this provision when he selected Gerald Ford for the office following Spiro Agnew's resignation in 1973. The following year, Ford became the second to do so when he chose Nelson Rockefeller to succeed him after he acceded to the presidency. As no mechanism existed for filling an intra-term vacancy in the vice presidency prior to 1967, the office was left vacant until filled through the next ensuing presidential election.

Throughout most of its history, American politics has been dominated by political parties. The Constitution is silent on the issue of political parties, and at the time it came into force in 1789, there were no parties. Soon after the 1st Congress convened, factions began rallying around dominant Washington administration officials, such as Alexander Hamilton and Thomas Jefferson. Greatly concerned about the capacity of political parties to destroy the fragile unity holding the nation together, Washington remained unaffiliated with any political faction or party throughout his eight-year presidency. He was, and remains, the only U.S. president never affiliated with a political party.^[18]

Three presidents held another U.S. federal office after serving as president.

Two presidents campaigned unsuccessfully for other U.S. state or federal elective offices after serving as president.

Many presidents have campaigned unsuccessfully for another term as president. Five did so after a gap of at least one term since they served:

Additionally, one former president, John Tyler, served in the government of the Confederate States during the American Civil War. Tyler served in the Provisional Confederate Congress from 1861 to 1862. He was elected to the Confederate House of Representatives in November 1861, but died before he could take his seat.