Porter Goss has resigned as CIA chief after less than two years in the role.
Mr Goss is a former congressman
President George W Bush made the surprise announcement, in which no reason for the move was given.
Mr Goss had been chosen by the president to replace George Tenet at the head of the US intelligence agency.
He was given the job of reforming the CIA after a series of intelligence failures, particularly in relation to the 11 September attacks.
Battle for change
Mr Goss had been at the helm of the agency only since September 2004.
He came under fire almost immediately, partly because he brought in several top aides from Congress, who were thought by some in the CIA to be too political.
In 2005 the CIA came under the authority of a new director of national intelligence, John Negroponte, after the inquiry into the 9/11 terror attacks.
There has been speculation that Mr Goss was not happy with the reduced access to the president he was afforded after the appointment of Mr Negroponte to oversee the work of all the intelligence agencies.
When he took the job he used to present the president with a daily intelligence briefing, but that task has since been taken away.
Several high-level CIA staff have resigned recently, amid rumblings of discontent at the CIA's headquarters in Virginia.
After graduating from Yale in 1960, the Connecticut-born Mr Goss worked for army intelligence and then for the CIA's directorate of operations.
In his speech announcing the nomination in 2004, President George W Bush referred to Mr Goss' CIA work "on two continents" - thought to be Europe and Latin America.
Although he does not go into details of his former CIA career, Mr Goss did once say he had "some very interesting moments in the Florida Straits" - a perceived reference to the Cuban missile crisis of 1962.
He served as a case officer for nine years but while suffering a serious infection in the 1970s, Mr Goss came to live in Florida with his wife, Mariel, to recuperate.
September 2001 probe
It was from Florida that he launched his political career, firstly in 1974 on the Sanibel City Council, then in 1983 on the Lee County Board of Commissioners.
He ran for Congress in 1988 and served there until 2004.
For eight years he was chairman of the House Intelligence Committee and also served on the House Rules Committee and House Select Committee for Homeland Security.
He joined with his counterpart in the Senate, Democrat Bob Graham, to lead a joint congressional inquiry into the intelligence failings surrounding the 9/11 attacks.
His CIA background and experience on the intelligence committee made him a favourite to succeed George Tenet as CIA director.
However, critics of Mr Goss said he was under the spell of Vice-President Dick Cheney and that his presence on the joint 9/11 inquiry gave the administration a deal of protection.