Born June 7, 1942 in the desert region of Sirte, Qaddafi's interest in politics was evident early in life. In 1961, he was expelled from school in Sebha for conspiring with classmates to carry out the political ideals of his idol, then-Egyptian President Gamal Abdel Nasser.
The young activist studied law at the University of Libya before entering the Military Academy of Benghazi in 1963 and finishing his training at the British Army Staff College. He returned from Britain in 1966 as an officer in the Signal Corps.
During his time in the Libyan military, Col. Qaddafi conspired with a group of fellow military officers to carry out the non-violent coup that would bring him into power. In the summer of 1969, Libya's King Idris I sought medical treatment in Greece and signed a decree naming his nephew, the Crown Prince Sayyid Hasan ar-Rida al-Mahdi as-Sanussi, as king, effective Sept. 2.
The crown prince was never appointed, however, because Qaddafi and his supporters seized power in a bloodless coup on Sept. 1.
In the early years of his leadership, Qaddafi used his position to call for a new era of Arab and Muslim unity. In a regime he termed "Islamic Socialism," Qaddafi emphasized Arab nationalism and popular democracy. While small business owners were allowed private control over their companies, larger organizations were owned by the Libyan government.
Qaddafi also led with a strong sense of Islamic moral expectation, outlawing alcohol and gambling. He summarized his leadership philosophy in the "Green Book," which was published in three volumes from 1975 until 1979.
In line with his vision of pan-Arab unity, Qaddafi made several attempts to bring together Arab nations. He established the Federation of Arab Republics, which included Libya, Egypt and Syria in 1972, but leaders of the countries were unable to agree to the terms of a regional union. Similar negotiating fallouts occurred during an attempted merger with Tunisia.
Throughout Qaddafi's leadership, Libya has experienced several regional and international confrontations, including a territorial dispute over the Aouzou Strip on the Libya-Chad border, and complications with Soviet weapons suppliers.
Meanwhile, Qaddafi's image as maverick leader continued to grow. His close ties with foreign organizations and his support of the Palestine Liberation Organization along with rebel movements in Sierra Leone and Liberia bolstered his reputation for backing liberation causes.
The Libyan leader also was accused of providing major financial backing for the "Black September Movement" that carried out the 1972 Munich Olympic bombings and perpetrated the bombing of the La Belle discotheque in Berlin in September 1986.
But it was Libya's connection to the crash of Pan Am Flight 103 in Lockerbie, Scotland on Dec. 21, 1988, that pushed the country into near diplomatic isolation. A bomb detonated in the plane's cargo hold as it flew from London to New York, killing all 259 passengers aboard, along with 11 people on the ground in Lockerbie.
Two men accused of being Libyan intelligence agents were charged in 1991 with planting the bomb; eventually, one was imprisoned for life and the other acquitted.
Libya was further implicated in the bombing of France's UTA Flight 772 over Niger in September 1989, which killed all 156 passengers and 14 crew members on board. The plane was bound for Paris from the Democratic Republic of the Congo with an intermediary stop in Chad. Similarities to the Lockerbie bombing led investigators to tie six Libyans to the bombing.
Media reports characterized Libya's possible motive for involvement in the attack as revenge against the French government for supporting Chad in a border dispute with Libya.
For many years, Libya resisted taking the blame for the Lockerbie bombing. But in a turnaround in 2003, Libya accepted responsibility for "the actions of its officials" in the bombing, renounced terrorism and agreed to pay the victims' families $2.7 billion.
David Mack, who was a State Department political officer in Libya when Qaddafi came to power, said in an Aug. 18, 2003 NewsHour interview that Qaddafi finally realized "that the rest of the world is moving ahead and Libya is falling farther and farther behind."
The move marked the beginning of a diplomatic transformation for Libya -- the United Nations lifted its sanctions imposed against the country for initially refusing to extradite the two intelligence officers.
"For [Qaddafi], this is a new beginning for Libya," said Mansour El-Kikhia, associate professor of political science and department chairman at the University of Texas at San Antonio. "And the cost of $2.8 billion was nothing compared to what he got in oil prices" once sanctions against oil investments were lifted.
Qaddafi, once called the "mad dog of the Middle East" by President Reagan, also began earning the praise of peace leaders such as South Africa's Nelson Mandela for his support of the Organization of African Unity, which later became the African Union.
Libya also announced a commitment to fight al-Qaida in 1999, and after the terrorist attacks on the United States on Sept. 11, 2001, Qaddafi was one of the most outspoken Muslim leaders against the al-Qaida perpetrators.
Then, in 2003, Qaddafi made the surprise announcement that he would dismantle his country's weapons of mass destruction programs and cooperate with international investigations. Three years later, the United States agreed to restore diplomatic relations with Libya for the first time in 25 years.
The cooperation in the war on terrorism, compensation for the Lockerbie victims' families and dismantling of weapons programs have improved the North African country's diplomatic ties and bolstered its overall economic standing.
The United States continued to further strengthen ties with Libya when, on Aug. 4, 2008, President Bush signed a law allowing the State Department to settle all remaining lawsuits against Libya by U.S. terrorism victims. Congress had blocked direct aid to Libya and the placement of a U.S. Embassy there until all U.S. victims had been paid.
Many expect that the Libyan leader will maintain power until his eldest son, Muhammad Qaddafi, now head of the Libyan Olympic Committee, succeeds him. Moammar Qaddafi is the father of eight children, several holding high-ranking government posts.