The following is a profile of Colin Powell, who has resigned from President George W. Bush's administration after serving four years as the country's first African-American secretary of state.

Colin Luther Powell was born to Jamaican parents in Harlem, New York, and grew up in the multi-ethnic Bronx, where he graduated from high school.

He entered the City College of New York to study geology and it was there, by his own account, that he found his calling when he joined the Reserve Officers Training Corps.

He called the army his "natural habitat," and two tours of Vietnam between 1962 and 1969 defined his ideas on war. What has become known as the Powell Doctrine is his belief that battles are "the politics of last resort".

Powell was commissioned a second lieutenant in the United States Army, and was one of the 16,000 military advisors dispatched to South Vietnam by President John F. Kennedy in 1962.

He was awarded a Purple Heart and the Bronze Star in 1963 in Vietnam. While serving a second tour of duty in Vietnam in 1968-1969, he received the Soldier's Medal for valor after he pulled fellow men from a helicopter wreckage.

Back from Vietnam, Powell earned an MBA from 1969 to 1971 at George Washington University in Washington, DC.

In the administration of President Jimmy Carter, Powell was an assistant to the deputy secretary of defense, and to the secretary of energy.

In 1987, Powell became the assistant to President Ronald Reagan for National Security Affairs. He was the first African-American to serve in this position, as he has been in every office he has held since.

Powell served under three presidents, Ronald Reagan, George Bush and Bill Clinton, as National Security Adviser. During the Clinton administration, he was appointed to the country's most senior military position, chairman of the Joint Chiefs of Staff, being the first black person and the youngest officer ever to hold the office.

In 1991, as chairman of the Joint Chiefs of Staff under President Bush, Powell became a national figure during the successful Desert Shield and Desert Storm operations which expelled the Iraqi army from Kuwait.

General Powell continued as chairman of the Joint Chiefs during the first months of the Clinton administration but retired from the military later and returned to private life.

At the time, his autobiography My American Journey was a national best-seller. Millions of Americans have been inspired by his life story, from his boyhood in the South Bronx, through service in Vietnam, to his term as assistant to the President for National Security Affairs.

In 2001, President George W. Bush appointed him Secretary of State, a position that placed him at the head of America's foreign policy. Since taking office he has taken a leading role in rallying America's allies and the United Nations to the war against terrorism.