The man with one of the most important roles in US foreign policy, Admiral William Fallon, has stepped down after less than a year in his job.
William Fallon is widely regarded as an astute commander
As head of the US Central Command (CentCom), Adm Fallon oversaw US strategy in the Middle East, North Africa and Central Asia.
The position put him in charge of an area covering Iraq, Afghanistan and Pakistan, making him one of the leading warriors in America's "war on terror".
But it was his perceived differences with his commander-in-chief, US President George W Bush, over another potential theatre of operations - Iran - that has led to his premature retirement.
The admiral was put under pressure by an article in Esquire magazine that portrayed him as a dissenter willing publicly to oppose the president's line on Iran.
Adm Fallon insisted he did not believe there were ever any differences about US policy objectives in the CentCom region.
"The simple perception that there is makes it difficult for me to effectively serve America's interests there," he said in a statement.
Adm Fallon's departure means the end of a distinguished career.
His appointment to head CentCom a year ago raised eyebrows not because he was thought unworthy, but because it was unusual for a navy man to be promoted to a post normally reserved for an army or marine general.
ADMIRAL WILLIAM FALLON
Born in New Jersey, 1944; raised a Roman Catholic
Became Naval pilot, flying missions in Vietnam
Served as commander in first Gulf War and in Nato's mission to Bosnia
Headed Pacific Command, then Central Command
The 63-year-old admiral, known as Fox - his call sign when he was a Navy fighter pilot - is highly regarded as an astute commander.
The fact that he was the first admiral in charge of US forces in the Middle East was seen as a sign that the Bush administration was looking to broaden its focus beyond Iraq to the wider Gulf, says the BBC's world affairs correspondent, Nick Childs.
Adm Fallon grew up in Merchantville, New Jersey, and graduated from Villanova University in 1967.
He was a navy combat pilot during the Vietnam War, commanded an attack squadron during the first Gulf War in 1991, and was involved in Nato's Operation Deliberate Force in Bosnia.
As head of Pacific Command from February 2005, he led a force of 300,000 personnel from all military services - representing about 20% of all US military forces on active duty.
He took an independent approach in his role, including encouraging military contacts with China, our correspondent says.
During Adm Fallon's year in charge of CentCom the outlook brightened in Iraq, with the surge policy of introducing more US troops leading to a fall in violence and increased stability.
But he was thought to be uneasy about the continuing high level of US troop numbers in Iraq - something that caused frictions with General David Petraeus, his more high-profile subordinate in the country, says our correspondent.
President Bush praised the admiral's record, saying: "He deserves considerable credit for progress that has been made... especially in Iraq and Afghanistan."
But that, it seems, was not enough to persuade his bosses that he should not be allowed to go.