Clay was never president, but had aspirations for that office, and played a pivotal role in the election of 1824, which was decided in the US House of Representatives. Clay was Speaker of the House at the time, and threw his support behind John Quincy Adams over Andrew Jackson, whom Clay hated. Adams won and shortly thereafter appointed Clay as his Secretary of State. Jackson's supporters called it a "corrupt bargain" and the ill-will it caused was one of the elements of Adam's defeat in 1828.
From the Library of Congress' American Memory series: "Representing the state of Kentucky in the U.S. Congress, Clay eloquently promoted the 'American System,' his plan to support domestic industry and agriculture (and reduce dependence on imports) through improved transportation routes, a protective tariff, and a national bank. In 1820, he negotiated the passage of the first of the three pieces of legislation that earned him the titles of the 'Great Pacificator' and the 'Great Compromiser.' The Missouri Compromise, the first piece of legislation, soothed the anxieties of both Southern and Northern factions by maintaining a balance between the number of states that permitted slavery and those that prohibited slavery.
"Clay was unsuccessful in his bid to become presidential candidate of the Democratic Republican Party in 1824. He then gave his support to John Quincy Adams and when Adams won the election, he appointed Clay secretary of state. Clay again failed in his bids to become the presidential candidate of the National Republican Party in 1832 and of the Whig Party in 1844. His opposition to the annexation of Texas—because the state's entry into the Union would have upset the balance of slave and free states—cost him the presidential election of 1844. Nonetheless, he remained a guiding force in American political life, exercising leadership in both the House and the Senate."