U.S. President Barack Obama on Thursday announced major changes to his national security team, including the nomination of CIA director Leon Panetta to replace Defense Secretary Robert Gates.
Here is a brief look at key members of the president's new team.
Robert Gates
Outgoing U.S. Defense Secretary Robert Gates is the only defense chief in U.S. history to be asked to remain in the post by a newly elected president.
He was sworn in under President Barack Obama's predecessor, George W. Bush, in 2006.
In the early 1990s, Gates served as the head of the U.S. Central Intelligence Agency. He is the only career officer in CIA history to rise from entry-level employee to director. Gates joined the agency in 1966, spending nearly three decades as an intelligence professional.
He served nearly nine years on the White House National Security Council, and was deputy national security adviser for President George H.W. Bush.
Before becoming defense secretary, Gates was the president of one of the nation's largest universities, Texas A&M - home to the George Bush School of Government and Public Service.
Leon Panetta
President Obama's nominee for new U.S. defense secretary, Leon Panetta, has a long history in the U.S. government.
Director of the Central Intelligence Agency since 2009, Panetta also served as Chief of Staff to President Bill Clinton in the 1990s, and before that headed the White House budget office under Mr. Clinton.
The long-time Democrat was elected to his first of eight terms in the U.S. House of Representatives in 1976, representing a district in California.
Following a stint as an Army intelligence officer, Panetta started out his political career working for Republicans, eventually becoming head of the Office for Civil Rights under President Richard Nixon. He left the post because of a disagreement and switched to the Democratic Party in 1971.
General David Petraeus
President Obama's pick to head the CIA, General David Petraeus, has held leadership roles in the wars in both Iraq and Afghanistan.
He became the commander of U.S. and NATO forces in Afghanistan in July of last year, and previously headed U.S. Central Command for nearly two years, overseeing a region including Afghanistan, Iraq, Pakistan and Yemen.
Before that, General Petraeus commanded U.S. and coalition forces in Iraq, presiding over the 2007 surge in American troops. He is widely credited with turning around the Iraq war and pulling the country back from the brink of a full-fledged sectarian war.
The four-star general also oversaw the development of the counterinsurgency manual for U.S. armed forces, which is the root of the Afghan war strategy.
Ryan Crocker
President Obama's choice to become the next U.S. ambassador to Afghanistan, Ryan Crocker, is a veteran U.S. diplomat with extensive experience across the Middle East.
He has served as a U.S. ambassador five previous times, starting in Lebanon in the early 1990s. After that, he became the U.S. ambassador to Kuwait, followed by Syria and Pakistan, and from 2007 to 2009, Iraq.
Crocker has also held the post of Deputy Assistant Secretary of State for Near Eastern Affairs.
After joining the foreign service in 1971, Crocker completed assignments in Iran, Qatar, Iraq, Egypt and Washington. He was assigned to the U.S. embassy in the Lebanese capital, Beirut, during the Israeli invasion of Lebanon in 1982 and the bombings of the embassy and Marine barracks in 1983.
In 2009, he received the Presidential Medal of Freedom, the nation's highest civilian award.
Lieutenant General John Allen
The nominee to replace General Petraeus as Afghanistan commander, Lieutenant General John Allen, is a long-serving military commander and instructor, who has received a number of military honors.
Allen is currently the deputy commander of U.S. Central Command, which covers a region including Afghanistan, Iraq, Pakistan and Yemen.
He was the first Marine Corps officer inducted as a term member of the Council on Foreign Relations.
In 2002, he became the first Marine Corps officer to serve in the Naval Academy as the Commandant of Midshipmen.
