Hawkish US Defence Secretary Donald Rumsfeld - the most prominent public advocate of the Bush administration's global war on terror and its campaign in Iraq - has resigned in the aftermath of Republican losses in mid-term elections.
President George W Bush asked him to stay on in his job after his re-election in November 2004 - a mark of the president's faith in the tough-talking man seen as a key architect of the war on Saddam Hussein.
Yet while the 74-year-old has a reputation as a great survivor, his job became increasingly bruising amid the turbulence in post-war Iraq.
... as we know, there are known knowns; there are things we know we know. We also know there are known unknowns ...
In April 2006 he faced an unprecedented challenge to his leadership after a number of retired generals sharply criticised him for disregarding military advice and ruling his department by intimidation.
And until 8 November - one day after the mid-terms, he had the same steadfast backing from the president that he did when he twice offered to resign during a crisis in 2004 over prisoner abuse at Abu Ghraib in Iraq.
But as Republicans lost the House of Representatives after a campaign dominated by Iraq, Mr Bush accepted Mr Rumsfeld's resignation.
"After a series of thoughtful conversations, Secretary Rumsfeld and I agreed that the timing is right for new leadership at the Pentagon," Mr Bush told reporters before going on to praise his close ally.
"Donald Rumsfeld has been a superb leader during a time of change, yet he also appreciates the value of bringing in a fresh perspective during a critical period of this war."
Donald Rumsfeld, the former Princeton University wrestler weathered many storms in the past, and wrote the maxim: "If you are not criticised, you are not doing your job."
Correspondents describe Mr Rumsfeld as strong and resilient - a genuine political veteran.
1962: House of Representatives
1969: Various roles serving Nixon administration
1973: Ambassador to Nato
1974: Chief of staff to Gerald Ford
1975: Defence secretary to Ford
1983: Visits Iraq and meets Saddam Hussein as US repairs relations with Baghdad
2001: Defence secretary
2006: Resigns the defence portfolio
He has been both the youngest and the oldest defence secretary in US history, first serving in the role under Gerald Ford between 1975 and 1977.
And he was probably also the most controversial.
He admitted in December 2004 to using a machine to replicate his signature on condolence letters to the families of dead soldiers, sparking criticism from army veterans.
Earlier in the month, a US marine publicly chided him over apparently inadequate equipment provided to soldiers going into combat.
He also faced criticism after casting doubt on whether there was ever a relationship between Saddam Hussein and al-Qaeda - contradicting an argument used to justify the attack on Iraq.
"To my knowledge, I have not seen any strong, hard evidence that links the two," he said - though he later issued a statement saying he had been misunderstood.
He gave fewer Pentagon news conferences in the aftermath of the Abu Ghraib scandal in April 2004 - prompting speculation that he was out of favour because of his handling of the crisis.
Before the 11 September 2001 attacks, his great project of transforming the US military into a lighter, more mobile force had run into trouble. He had offended powerful groups on Capitol Hill, not to mention much of the military top brass.
Mr Rumsfeld predicted Iraq would be a "hard slog". The newspapers began to speculate about his successor.
But following the attacks on New York and Washington, and a dramatically successful campaign in Afghanistan, his stock rose.
Winning the war in Iraq appeared to be another success for the Rumsfeld doctrine of deploying lighter, less numerous, but technologically highly capable forces.
But he upset some European countries with his frankness - dismissing French and German scepticism over the US attack on Iraq as the voice of "old Europe".
His Pentagon has largely had stewardship over Iraq. If things have gone badly there, then it is hard to place the blame for the latest crisis elsewhere, critics say.
Mr Rumsfeld has also faced the task of redirecting the strategy and arsenal of the world's largest military power to take on the invisible, stateless enemy of global terrorism for what the US military has branded the "Long War".
But his ability to complete such broader goals may have been compromised by the damage Iraq had done to his reputation, analysts said.
He was, however, known as a tough and determined character with the huge personal resources needed to cope with the rigours of his brief.
He wrote a pamphlet known as Rumsfeld's Rules - famous in US political circles - which collects nearly 30 years' worth of quotations and reflections by himself and others.
In a chapter titled "Keeping Your Bearings in the White House", one entry reads: "If you are not criticised, you are not doing your job."
Another, in a chapter headed "Serving in Government", states: "If in doubt, don't. If still in doubt, do what's right."
Mr Rumsfeld's former deputy, Paul Wolfowitz, once described him as "a constant, active source of energy... he generates a mini-storm wherever he goes".
Henry Kissinger once said that Mr Rumsfeld was the most ruthless man he knew, adding that he was a "skilled full-time politician-bureaucrat in whom ambition, ability and substance fuse seamlessly".
Mr Rumsfeld spent three years in the US navy before starting out his political career as an assistant to a congressman.
Twenty years and several jobs later, he was appointed defence secretary for the first time - nearly 25 years before he took the post under George W Bush.
Much of the time between was spent in big business, including stints as chief executive officer of pharmaceutical company GD Searle & Co, CEO of General Instrument Corporation and Chairman of Gilead Sciences.
But he also continued to advise Republican administrations and exercise his influence over issues of defence throughout the 1980s and 1990s.