The President of the United States of America (acronym: POTUS) is the head of state and head of government of the United States. The president leads the executive branch of the federal government and is the commander-in-chief of the United States Armed Forces.

Article II of the U.S. Constitution vests the executive power of the United States in the president and charges him with the execution of federal law, alongside the responsibility of appointing federal executive, diplomatic, regulatory, and judicial officers, and concluding treaties with foreign powers, with the advice and consent of the Senate. The president is further empowered to grant federal pardons and reprieves, and to convene and adjourn either or both houses of Congress under extraordinary circumstances. Since the founding of the United States, the power of the president and the federal government have grown substantially and each modern president, despite possessing no formal legislative powers beyond signing or vetoing congressionally passed bills, is largely responsible for dictating the legislative agenda of his party and the foreign and domestic policy of the United States. The president is frequently described as the most powerful person in the world.

The United States of America (commonly abbreviated to the United States, the U.S., the USA, America, and the States) is a federal constitutional republic comprising fifty states and a federal district. The country is situated mostly in central North America, where its forty-eight contiguous states and Washington, D.C., the capital district, lie between the Pacific and Atlantic Oceans, bordered by Canada to the north and Mexico to the south. The state of Alaska is in the northwest of the continent, with Canada to the east and Russia to the west, across the Bering Strait. The state of Hawaii is an archipelago in the mid-Pacific. The country also possesses several territories in the Pacific and Caribbean.

At 3.79 million square miles (9.83 million km²) and with over 312 million people, the United States is the third or fourth largest country by total area, and the third largest by both land area and population. It is one of the world's most ethnically diverse and multicultural nations, the product of large-scale immigration from many countries. The U.S. economy is the world's largest national economy, with an estimated 2011 GDP of $15.1 trillion (22% of nominal global GDP and over 19% of global GDP at purchasing-power parity). Per capita income is the world's sixth-highest.

Barack Hussein Obama II (ⁱ/bəˈrɑːk huːˈseɪn oʊˈbɑːmə/; born August 4, 1961) is the 44th and current President of the United States. He is the first African American to hold the office. In January 2005, Obama was sworn in as a U.S. Senator in the state of Illinois. He would hold this office until November 2008, when he resigned following his victory in the 2008 presidential election.

Born in Honolulu, Hawaii, Obama is a graduate of Columbia University and Harvard Law School, where he was the president of the Harvard Law Review. He was a community organizer in Chicago before earning his law degree. He worked as a civil rights attorney in Chicago and taught constitutional law at the University of Chicago Law School from 1992 to 2004. He served three terms representing the 13th District in the Illinois Senate from 1997 to 2004.

Following an unsuccessful bid against the Democratic incumbent for a seat in the United States House of Representatives in 2000, Obama ran for the United States Senate in 2004. Several events brought him to national attention during the campaign, including his victory in the March 2004 Illinois Democratic primary for the Senate election and his keynote address at the Democratic National Convention in July 2004. He won election to the U.S. Senate in Illinois in November 2004. His presidential campaign began in February 2007, and after a close campaign in the 2008 Democratic Party presidential primaries against Hillary Rodham Clinton, he won his party's nomination. In the 2008 presidential election, he defeated Republican nominee John McCain, and was inaugurated as president on January 20, 2009. Nine months later, Obama was named the 2009 Nobel Peace Prize laureate. In April 2011, he announced that he would be running for re-election in 2012.

Ronald Wilson Reagan ( /ˈrɒnəld ˈwɪlsən ˈreɪɡən/; February 6, 1911 – June 5, 2004) was the 40th President of the United States, serving from 1981 to 1989. Prior to that, he was the 33rd Governor of California from 1967 to 1975 and a radio, film and television actor.

Born in Tampico, Illinois and raised in Dixon, Reagan was educated at Eureka College, earning a Bachelor of Arts degree in economics and sociology. After his graduation, Reagan moved first to Iowa to work as a radio broadcaster and then in to Los Angeles in 1937 where he began a career as an actor, first in films and later television. Some of his most notable films include Knute Rockne, All American, Kings Row, and Bedtime for Bonzo. Reagan served as president of the Screen Actors Guild, and later as a spokesman for General Electric (GE); his start in politics occurred during his work for GE. Originally a member of the Democratic Party, his positions began shifting rightward in the late 1950s, and he switched to the Republican Party in 1962. After delivering a rousing speech in support of Barry Goldwater's presidential candidacy in 1964, he was persuaded to seek the California governorship, winning two years later and again in 1970. He was defeated in his run for the Republican presidential nomination in 1968 as well as 1976, but won both the nomination and general election in 1980, defeating incumbent Jimmy Carter.

William Jefferson "Bill" Clinton (born William Jefferson Blythe III; August 19, 1946) is an American politician who served as the 42nd President of the United States from 1993 to 2001. Inaugurated at age 46, he was the third-youngest president. He took office at the end of the Cold War, and was the first president of the baby boomer generation. Clinton has been described as a New Democrat. Many of his policies have been attributed to a centrist Third Way philosophy of governance.

Born and raised in Arkansas, Clinton became both a student leader and a skilled musician. He is an alumnus of Georgetown University where he was Phi Beta Kappa and earned a Rhodes Scholarship to attend the University of Oxford. He is married to Hillary Rodham Clinton, who has served as the United States Secretary of State since 2009 and was a Senator from New York from 2001 to 2009. Both Clintons received law degrees from Yale Law School, where they met and began dating. As Governor of Arkansas, Clinton overhauled the state's education system, and served as Chair of the National Governors Association.