Tributes have poured in from around the world for Sergio Vieira de Mello, the UN special envoy in Iraq, who was among those killed in the bombing of the UN's headquarters in Baghdad on Tuesday.
UN Secretary General Kofi Annan said there was "no-one we could less afford to spare [than Mr Vieira de Mello], or who would be more acutely missed throughout the UN system".
Iraq's Governing Council described the Brazilian diplomat as "a friend of the Iraqi people" and called for a monument to be named in his memory.
US Secretary of State Colin Powell called Mr Vieira de Mello "a hero who dedicated his life to helping people in danger".
Mr Powell said: "Sergio never shirked the most difficult assignments... Where others saw obstacles or despair, he created options and solutions."
Bertrand Ramcharan, who was deputising for Mr Vieira de Mello as UN high commissioner for human rights, said the diplomat was "an immensely gifted man".
"He was gifted by nature with intelligence, wit and charm, and to that he added a solid education and a solid commitment to the principles of the United Nations."
The UN High Commissioner for Refugees, Ruud Lubbers, recalled Mr Vieira de Mello as "a true gentleman who garnered the respect of adversaries, a tough negotiator who fought for human rights and the dignity of the downtrodden".
'A militant for peace'
Stunned staff at the UN human rights department in Geneva spoke of "a pall" over the office following Mr Vieira de Mello's death.
"Everybody is still in shock, and a bit traumatised. There is a great sense of sadness," said spokesman Jose Diaz.
Sérgio Pinheiro, head of the centre for Violence Studies in the University of Sao Paulo, knew Vieira de Mello for 25 years.
"We are extremely shocked," he said. "However, I recently talked with his secretary Nilmário Miranda and I was delighted to hear that official mourning has been decreed in Brazil."
Mr Pinheiro, who is in Geneva to carry out a study into child abuse, said Vieira de Mello always supported him in his actions in favour of human rights in Brazil.
Mr Pinheiro said the tragedy was made all the worse by the fact that Vieira de Mello was due to have returned to the High Commission at the beginning of September.
"It is an extraordinary shock. Not only for the loss, but also due to the enormous frustration, because he was soon going to return to Geneva", he said.
Hedayat Abdel-Nabi, president of the Geneva UN correspondents association, called Mr Vieira de Mello "the best of the best - a charismatic, brilliant character".
Countries across Asia, where Mr Vieira de Mello served for many years, also lined up to honour the fallen diplomat.
East Timor President Xanana Gusmao, whose country Mr Vieira de Mello helped steer to independence, said: "Our nation mourns the death of a unique and unforgettable friend.
"He fought tirelessly for democracy, human rights and sustainable justice for the people of East Timor."
Indonesia - East Timor's former ruler - said Mr Vieira de Mello "personified the high dedication and bravery of those serving humanity under the banner of the UN, often in most difficult circumstances".
1981: Adviser to UN forces, Lebanon
1996: Humanitarian co-ordinator, Rwanda
1999: Special representative for Kosovo
2000: Head of UN operations, East Timor
2002: UN commissioner for human rights
2003: UN special representative in Iraq
Cambodia's King Norodom Sihanouk said Mr Vieira de Mello "helped and served the peoples of every country in the
world, including Cambodia, with self-sacrifice, efficiency and limitless devotion and without seeking any personal gain or glory".
In Europe, France's Bernard Kouchner, who succeeded Mr Vieira de Mello at the head of the UN administration in Kosovo in 1999, said he did not die in vain.
"He died for us like a militant, not an international civil servant - a militant for peace and human rights."