The Nobel committee bestowed the prestigious award for 2005 on Mohamed ElBaradei, the UN official who rose to prominence by exposing the lengths that America would go to in its efforts to build a case for war.
Mr ElBaradei, the director general of the International Atomic Energy Agency (IAEA), which shares the prize, delivered a body blow to the Bush administration on the eve of the Iraq war.
During a televised meeting of the UN Security Council in March 2003, he told assembled foreign ministers that documents purporting to prove Iraq had attempted to import uranium from Niger to make a nuclear weapon were fake.
Leading lights of the Bush administration, particularly Condoleezza Rice and Vice-President Dick Cheney, had advanced Iraq's supposed nuclear weapons programme as a major reason for going to war.
Ms Rice memorably said of the UN weapons inspectors' search for a "smoking gun" before the war: "We don't want the smoking gun to be a mushroom cloud." Britain also cited the now discredited Niger connection to push the case for immediate military action against Saddam, suggesting that he was in the process of adding a nuclear capacity to his arsenal of weapons of mass destruction.
No weapons of mass destruction of any sort, far less any evidence of a nuclear programme, have ever been discovered.
The recognition of Mr ElBaradei and the IAEA is also seen as a warning to President Bush- and to Tony Blair who backed Mr Bush over the invasion - against military strikes on Iran over its nuclear programme.
The underlying message of the Nobel committee, which said the threat of nuclear weapons "must be met through the broadest possible international co-operation", is that weapons inspections are a better way of dealing with any crisis than war.
The decision, which came on the 60th anniversary of the American atomic bomb strikes on Hiroshima and Nagasaki, signals a move by the Nobel committee in Norway to return to its disarmament roots.
"This is a message to all the people of the world: Do what you can to get rid of nuclear weapons," said the committee chairman, Ole Danbolt Mjoes, as he announced the prize. "The people's power is formidable."
Egyptian-born Mr ElBaradei, who learned of the award as he was watching television at home with his wife, declared that the prize would be "a shot in the arm" for the IAEA, now sidelined over the nuclear ambitions of Iran and North Korea, the countries posing the biggest nuclear threat to world peace and security. The IAEA has also been refused access to the architect of Pakistan's nuclear bomb, Abdul Qadeer Khan, who is now under house arrest.
Mr Khan was the informal CEO of an illicit nuclear supermarket that had dealings with more than 30 companies in 30 countries, and who passed nuclear secrets to North Korea and Libya.
Mr ElBaradei said at IAEA headquarters in Vienna: "The award sends a very strong message: 'Keep doing what you are doing - be impartial, act with integrity', and that is what we intend to do."
Mr ElBaradei said, to applause from UN staff: "The advantage of having this recognition today, it will strengthen my resolve."
He said the prize was a recognition that "the number one danger we are facing today" comes from the threat of nuclear weapons proliferation.
Described as a "fearless advocate" of disarmament, Mr ElBaradei's power is that he will not shy from telling politicians the unpalatable truth, based on spin-free verified evidence from on-the-ground inspections.
However it was not the IAEA, but Iranian defectors who first sounded the alarm about Iran's clandestine nuclear programme.
Investigations by the UN weapons inspectors proved Iran had been working on a nuclear programme for 18 years before they were caught red-handed.
Even now, after years of inspections, the IAEA has not decided conclusively that they are working on a weapons programme, which in any case they deny. On North Korea, the IAEA can only guess what is going on in the hermit regime because inspectors were thrown out in 2002.
Disarmament negotiations with Pyongyang have now, in effect, been taken over by six-party talks involving regional players and the United States.
Mr ElBaradei is the enforcer of the Nuclear Non-Proliferation Treaty (NPT) regime. Since taking over as director-general of the IAEA in 1997,after moving up through the organisation during 13 years, he has particularly lambasted what he sees as double standards on the part of countries that have nuclear weapons, but which seek to prevent others from procuring them.
"We must abandon the unworkable notion that it is morally reprehensible for some to pursue weapons of mass destruction, yet morally acceptable for others to rely on them for security - and indeed to continue to refine their capacities and postulate plans for their use," he said.
Mr ElBaradei's award is unlikely to please the Americans, who are working with the IAEA in hopes of referring Tehran to the UN Security Council for failing to come clean on the full extent of its nuclear programme.
John Bolton, now the US ambassador to the UN, launched an unsuccessful campaign to unseat Mr ElBaradei when Mr Bolton was still the top US official responsible for disarmament. But Mr ElBaradei has just been confirmed for a third term as the rest of the board, including Britain, rallied round his candidacy and the US withdrew its objection.