Ronald Ernest Paul (born August 20, 1935) is an American author, activist, medical doctor, and politician who served as the U.S. representative for Texas's 22nd congressional district from 1976 to 1977, and again from 1979 to 1985, as well as for Texas's 14th congressional district from 1997 to 2013. On three occasions, he sought the presidency of the United States, first as the Libertarian Party nominee in 1988, and then as a candidate for the Republican Party in 2008 and 2012.

A self-described constitutionalist, Paul is a critic of several of the federal government's policies, especially the existence of the Federal Reserve and tax policy, as well as the military–industrial complex, the war on drugs, and the war on terror. He has also been a vocal critic of mass surveillance policies such as the Patriot Act and the NSA surveillance programs. In 1976, Paul formed the Foundation for Rational Economics and Education (FREE), and in 1985 was named the first chairman of the conservative PAC Citizens for a Sound Economy, both free-market groups focused on limited government. He has been characterized as the "intellectual godfather" of the Tea Party movement, a fiscally conservative political movement started in 2007 and popularized in 2009 that is largely against most matters of interventionism.

Paul served as a flight surgeon in the U.S. Air Force from 1963 to 1968, and worked as an obstetrician-gynecologist from the 1960s to the 1980s. When his son, Rand Paul, was elected as a U.S. senator from Kentucky in 2011, Paul became the first U.S. representative in history to serve concurrently with a child in the Senate. He is a senior fellow and distinguished counselor of the Mises Institute, and has published a number of books and promoted the ideas of economists of the Austrian School, such as Murray Rothbard, Friedrich Hayek, and Ludwig von Mises, during his political campaigns. He has cited President Grover Cleveland as his preferred model of presidency.

After the popularity and grassroots enthusiasm of his 2008 presidential bid, Paul announced in July 2011 that he would not seek reelection to Congress in order to focus on his 2012 bid for the presidency. Finishing in the top four with delegates in both races (while winning four states in the 2012 primaries), he refused to endorse the Republican nominations of John McCain and Mitt Romney during their respective 2008 and 2012 campaigns against Barack Obama. In May 2012, Paul announced that he would not be competing in any other presidential primaries but that he would still compete for delegates in states where the primary elections had already been held. At both the 2008 and 2012 Republican National Conventions, Paul received the second-highest number of delegates, behind only McCain and Romney, respectively.

Paul remained active after his retirement from electoral politics, giving speeches promoting libertarian and libertarian-conservative ideas on college campuses. He also continues to provide political commentary through The Ron Paul Liberty Report, a web show he co-hosts on YouTube. At 81, and despite not running, Paul received one electoral vote from a Texas faithless elector in the 2016 presidential election, making him the oldest person to receive an Electoral College vote, as well as the second registered Libertarian presidential candidate in history to receive an electoral vote, after John Hospers in 1972.

Ronald Ernest Paul was born on August 20, 1935, in Pittsburgh, the son of Howard Caspar Paul (1904–1997), who ran a small dairy company, and Margaret Paul (née Dumont; 1908–2001). His paternal grandfather emigrated from Germany, and his paternal grandmother, a devout Christian, was a first-generation German American. Ron Paul has two older brothers, William and David, and two younger brothers, Jerrold and Wayne. As a junior at suburban Dormont High School, he was the 200-meter dash state champion. Paul went to Gettysburg College, where he was a member of the Lambda Chi Alpha fraternity. He graduated with a B.S. degree in biology in 1957.

Paul earned a Doctor of Medicine degree from Duke University's School of Medicine in 1961, and completed his medical internship at the Henry Ford Hospital in Detroit and his residency in obstetrics and gynecology at Magee-Womens Hospital in Pittsburgh. Paul served as a flight surgeon in the United States Air Force from 1963 to 1965 and then in the United States Air National Guard from 1965 to 1968. Paul and his wife then relocated to Texas, where he began a private practice in obstetrics and gynecology. One child that he helped deliver was famous Tejano singer Selena Quintanilla.

While a medical resident in the 1960s, Paul was influenced by Friedrich Hayek's The Road to Serfdom, which caused him to read other publications by Ludwig von Mises and Ayn Rand. He came to know economists Hans Sennholz and Murray Rothbard well, and credits his interest in the study of economics to them. When President Richard Nixon "closed the gold window" by ending American participation in the Bretton Woods System, thus ending on August 15, 1971, the U.S. dollar's loose association with gold, Paul decided to enter politics, and became a Republican candidate for the United States Congress.