Barack Hussein Obama II (born August 4, 1961) is the 44th and current President of the United States. He is the first African American to hold the office. Obama previously served as the junior United States Senator from Illinois, from January 2005 until he resigned after his election to the presidency in November 2008.
Obama's 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 general election, he defeated Republican nominee John McCain and was inaugurated as president on January 20, 2009. Obama is also the 2009 Nobel Peace Prize laureate.

George Washington (February 22, 1732 - December 14, 1799) was the commander of the Continental Army in the American Revolutionary War (1775–1783) and the first President of the United States of America (1789–1797). For his central role in the formation of the United States, he is often referred to as "the father of his country".

Abraham Lincoln (February 12, 1809 – April 15, 1865) served as the 16th President of the United States from March 1861 until his assassination in April 1865. He successfully led his country through its greatest internal crisis, the American Civil War, preserving the Union and ending slavery. Before his election in 1860 as the first Republican president, Lincoln had been a country lawyer, an Illinois state legislator, a member of the United States House of Representatives, and twice an unsuccessful candidate for election to the U.S. Senate. As an outspoken opponent of the expansion of slavery in the United States, Lincoln won the Republican Party nomination in 1860 and was elected president later that year. His tenure in office was occupied primarily with the defeat of the secessionist Confederate States of America in the American Civil War. He introduced measures that resulted in the abolition of slavery, issuing his Emancipation Proclamation in 1863 and promoting the passage of the Thirteenth Amendment to the Constitution. Six days after the large-scale surrender of Confederate forces under General Robert E. Lee, Lincoln became the first American president to be assassinated.

Franklin Delano Roosevelt (January 30, 1882 – April 12, 1945) was the 32nd President of the United States and a central figure in world events during the mid-20th century, leading the United States during a time of worldwide economic crisis and world war. The only American president elected to more than two terms, he was often referred to by his initials, FDR. Roosevelt won his first of four presidential elections in 1932, while the United States was in the depths of the Great Depression. FDR's combination of optimism and economic activism is often credited with keeping the country's economic crisis from developing into a political crisis. He led the United States through most of World War II, and died in office of a cerebral hemorrhage, shortly before the war ended.

James Madison (March 16, 1751 – June 28, 1836) was an American politician and political philosopher who served as the fourth President of the United States (1809–1817) and is considered one of the Founding Fathers of the United States. The "Father of the Constitution," he was the principal author of the document. In 1788, he wrote over a third of the Federalist Papers, still the most influential commentary on the Constitution. The first president to have served in the United States Congress, he was a leader in the 1st United States Congress, drafting many basic laws, and was responsible for the first ten amendments to the Constitution (said to be based on the Virginia Declaration of Rights) and thus is also known as the "Father of the Bill of Rights". As a political theorist, Madison's most distinctive belief was that the new republic needed checks and balances to protect individual rights from the tyranny of the majority.

Andrew Jackson (March 15, 1767 – June 8, 1845) was the seventh President of the United States (1829–1837). He was military governor of Florida (1821), commander of the American forces at the Battle of New Orleans (1815), and eponym of the era of Jacksonian democracy. A polarizing figure who dominated American politics in the 1820s and 1830s, his political ambition combined with widening political participation, shaping the modern Democratic Party.
His legacy is now seen as mixed, as a protector of popular democracy and individual liberty for white male citizens, checkered by his support for Indian removal and slavery. Renowned for his toughness, he was nicknamed “Old Hickory." As he based his career in developing Tennessee, Jackson was the first president primarily associated with the American frontier.

James Knox Polk (November 2, 1795 – June 15, 1849) was the 11th President of the United States (1845–1849). Polk was born in Mecklenburg County, North Carolina. He later lived in and represented the state of Tennessee. A Democrat, Polk served as Speaker of the House (1835–1839) and Governor of Tennessee (1839–1841) before becoming president.

A firm supporter of Andrew Jackson, Polk was the last strong pre-Civil War president. Polk is noted for his foreign policy successes. He threatened war with Britain then backed away and split the ownership of the Northwest with Britain. He is more famous for leading the nation into the Mexican–American War, in which the US was victorious. He lowered the tariff and established a treasury system that lasted until 1913.

Thomas Woodrow Wilson (December 28, 1856 – February 3, 1924) was the 28th President of the United States. A leading intellectual of the Progressive Era, he served as President of Princeton University from 1902 to 1910, and then as the Governor of New Jersey from 1911 to 1913. With Theodore Roosevelt and William Howard Taft dividing the Republican Party vote, Wilson was elected President as a Democrat in 1912.

In his first term, Wilson persuaded a Democratic Congress to pass the Federal Reserve Act, Federal Trade Commission, the Clayton Antitrust Act, the Federal Farm Loan Act and America's first-ever federal progressive income tax in the Revenue Act of 1913. Wilson brought many white Southerners into his administration, and tolerated their expansion of segregation in many federal agencies

Harry S. Truman (May 8, 1884 – December 26, 1972) was the 33rd President of the United States (1945–1953). As President Franklin D. Roosevelt's third vice-president and the 34th Vice President of the United States, he succeeded to the presidency on April 12, 1945, when President Roosevelt died less than three months after beginning his fourth term.

Ronald Wilson Reagan (February 6, 1911– June 5, 2004) was the 40th President of the United States (1981–1989) and the 33rd Governor of California (1967–1975). Prior to his political career Reagan was also a famous motion picture actor and president of the Screen Actors Guild.
As president, Reagan implemented sweeping new political and economic initiatives. His supply-side economic policies, dubbed "Reaganomics", advocated reduced business regulation, controlling inflation, reducing growth in government spending, and spurring economic growth through tax cuts. In his first term he survived an assassination attempt, took a hard line against labor unions, and ordered military actions in Grenada. He was reelected in a landslide in 1984, proclaiming it was "Morning in America". His second term was primarily marked by foreign matters, namely the ending of the Cold War, the bombing of Libya, and the revelation of the Iran-Contra affair. Publicly describing the Soviet Union as an "evil empire", he supported anti-Communist movements worldwide and spent his first term forgoing the strategy of détente by ordering a massive military buildup in an arms race with the USSR. Reagan negotiated with Soviet General Secretary Mikhail Gorbachev, culminating in the INF Treaty and the decrease of both countries' nuclear arsenals.

William Jefferson "Bill" Clinton (born William Jefferson Blythe III, August 19, 1946) was the 42nd President of the United States from 1993 to 2001. He was the third-youngest president; only Theodore Roosevelt and John F. Kennedy were younger when entering office. He became president at the end of the Cold War, and as he was born in the period after World War II, he is known as the first Baby Boomer president. His wife, Hillary Rodham Clinton, is currently the United States Secretary of State. She was previously a United States Senator from New York, and also candidate for the Democratic presidential nomination in 2008. Both are graduates of Yale Law School.

Clinton was described as a New Democrat and was largely known for the Third Way philosophy of governance that came to epitomize his two terms as president. His policies, on issues such as the North American Free Trade Agreement and welfare reform, have been described as centrist. Clinton presided over the longest period of peace-time economic expansion in American history, which included a balanced budget and a federal surplus. The Congressional Budget Office reported a surplus of $236B in 2000, the last full year of Clinton's presidency. On the heels of a failed attempt at health care reform with a Democratic Congress, Republicans won control of the House of Representatives for the first time in forty years. Two years later, in 1996, Clinton was re-elected and became the first member of the Democratic Party since Franklin D. Roosevelt to win a second term as president. Later he was impeached for obstruction of justice, but was subsequently acquitted by the U.S. Senate.

John Fitzgerald "Jack" Kennedy (May 29, 1917 – November 22, 1963), often referred to by his initials JFK, was the 35th President of the United States, serving from 1961 until his assassination in 1963.

After Kennedy's military service as commander of the Motor Torpedo Boat PT-109 during World War II in the South Pacific, his aspirations turned political. With the encouragement and grooming of his father, Joseph P. Kennedy, Sr., Kennedy represented Massachusetts's 11th congressional district in the U.S. House of Representatives from 1947 to 1953 as a Democrat, and served in the U.S. Senate from 1953 until 1960. Kennedy defeated then Vice President and Republican candidate Richard Nixon in the 1960 U.S. presidential election, one of the closest in American history. He was the second-youngest President (after Theodore Roosevelt), the first President born in the 20th century, and the youngest elected to the office, at the age of 43. Kennedy is the first and only Catholic and the first Irish American president, and is the only president to have won a Pulitzer Prize. Events during his administration include the Bay of Pigs Invasion, the Cuban Missile Crisis, the building of the Berlin Wall, the Space Race, the African American Civil Rights Movement and early events of the Vietnam War.