Barack Hussein Obama II ( bə-RAHK hoo-SAYN oh-BAH-mə; born August 4, 1961) is an American politician who served as the 44th president of the United States from 2009 to 2017. A member of the Democratic Party, he was the first African-American president. Obama previously served as a U.S. senator representing Illinois from 2005 to 2008 and as an Illinois state senator from 1997 to 2004, and worked as a civil rights lawyer and university lecturer.

Obama was born in Honolulu, Hawaii. He attended Occidental College and transferred to finish his undergraduate studies at Columbia University, graduating in 1983. He later worked as a community organizer in Chicago. In 1988, Obama enrolled in Harvard Law School, where he was the first black president of the Harvard Law Review. He became a civil rights attorney and an academic, teaching constitutional law at the University of Chicago Law School from 1992 to 2004. He also went into elective politics. Obama represented the 13th district in the Illinois Senate from 1997 until 2004, when he successfully ran for the U.S. Senate. In 2008, after a close primary campaign against Hillary Clinton, he was nominated by the Democratic Party for president and chose Joe Biden as his running mate. Obama was elected president, defeating Republican nominee John McCain in the presidential election and was inaugurated on January 20, 2009. Nine months later, he was named the 2009 Nobel Peace Prize laureate, a decision that drew a mixture of praise and criticism.

Obama's first-term actions addressed the global financial crisis and included a major stimulus package to guide the economy to recover from the Great Recession, a partial extension of George W. Bush's tax cuts, legislation to reform health care, a major financial regulation reform bill, and the end of a major U.S. military presence in Iraq. Obama also appointed Supreme Court justices Sonia Sotomayor and Elena Kagan, the former being the first Hispanic American on the Supreme Court. He ordered the counterterrorism raid which killed Osama bin Laden and downplayed Bush's counterinsurgency model, expanding air strikes and making extensive use of special forces while encouraging greater reliance on host-government militaries. Obama also ordered military involvement in Libya in order to implement UN Security Council Resolution 1973, contributing to the overthrow of Muammar Gaddafi.

After winning re-election by defeating Republican opponent Mitt Romney, Obama was sworn in for a second term on January 20, 2013. In his second term, Obama took steps to combat climate change, signing a major international climate agreement and an executive order to limit carbon emissions. Obama also presided over the implementation of the Affordable Care Act and other legislation passed in his first term, and he negotiated a nuclear agreement with Iran and normalized relations with Cuba. The number of American soldiers in Afghanistan fell dramatically during Obama's second term, though U.S. soldiers remained in the country throughout Obama's presidency. Obama promoted inclusion for LGBT Americans, culminating in the Supreme Court's decision to strike down same-sex marriage bans as unconstitutional in Obergefell v. Hodges.

Obama left office on January 20, 2017, and continues to reside in Washington, D.C. His presidential library in Chicago began construction in 2021. Since leaving office, Obama has remained active in Democratic politics, including campaigning for candidates in various American elections, such as his former vice president Joe Biden in his successfull bid for president in 2020. Outside of politics, Obama has published three bestselling books: Dreams from My Father (1995), The Audacity of Hope (2006) and A Promised Land (2020). Rankings by scholars and historians, in which he has been featured since 2010, place him in the middle to upper tier of American presidents.