Once known as a diplomatic rock star, Kofi Annan, who leaves office as United Nations secretary-general on Sunday after a decade on the job, exudes dignity, compassion and modesty - qualities that make him easy to romanticise.

But after he won the Nobel Peace Prize in 2001, he faced mounting bad news - the war in Iraq which he opposed, lingering questions on UN scandals, deteriorating ties with the Bush administration and US right-wingers calling for his head.

"Words he spoke during the first three or four years were the single most important and the most lasting: Human rights and a humanitarian agenda," said James Traub, author of a recent book on Mr Annan, The Best Intentions.

"In the second term, virtually everything failed that he tried to do or things that were done to him," Mr Traub said.

Mr Annan, a 68-year-old Ghanaian and career UN official, lists his main achievements as establishing the concept of a responsibility to protect civilians when their rulers will not or cannot. He also ranks high his struggle against poverty.

"In a world where you have extreme poverty and immense wealth sitting side by side, it's not sustainable," Mr Annan said pointing to the UN's Millennium Development Goals, that set targets to reduce poverty and raise educational levels.

His worst moments, Mr Annan said, included not being able to stop the bloodshed in Sudan's Darfur, the oil-for-food debacle and the Iraq war, after which he lost his voice for months.

Then came the most painful event - the bombing of UN headquarters in Baghdad on August 19, 2003 that killed 22 people after Mr Annan had decided, at the urging of the United States, to send senior UN staff back to Iraq.

"It hit me almost as much as the loss of my twin sister," Mr Annan told his last news conference, his voice choking. Efua Annan died of an illness in 1991.

In 2003, the oil-for-food scandal also broke, with Saddam Hussein having bilked the $64 billion program designed to relieve the pain of UN sanctions on ordinary Iraqis. The sanctions were imposed after Baghdad's troops invaded Kuwait.

While few UN officials were accused of enriching themselves, the world body was blamed for lax management and not blowing the whistle on Saddam's tactics.

Factbox

Secretaries-general of the United Nations

Following is a list of secretaries-general of the United Nations:
• 1946-1952 - Trygve Lie of Norway
• 1953-1961 - Dag Hammarskjold of Sweden
• 1961-1971 - U Thant of Burma (now Myanmar)
• 1972-1981 - Kurt Waldheim of Austria
• 1982-1991 - Javier Perez de Cuellar of Peru
• 1992-1996 - Boutros-Ghali of Egypt
• 1997-2006 - Kofi Annan of Ghana
• 2007-____ - Ban Ki-Moon of South Korea.