Annan was probed over corruption allegations.
UNITED NATIONS: Former UN chief Kofi Annan has played diplomatic poker with dictators ranging from Saddam Hussein to Omar al-Bashir, but the odds are stacked against him in taking on Syria's ruthless president.
Two terms as UN secretary general, during which he won the Nobel Peace Prize but was himself accused of corruption, taught the 73-year-old Ghanaian how to look after himself in international negotiations.
Eloquent and self-effacing, Annan left office at the end of 2006 as one of the most popular UN leaders ever.
"A real pro," was how Human Rights Watch's director Kenneth Roth described Annan after the announcement Thursday that the former UN leader would be the United Nations and Arab League's special envoy on the Syria crisis.
Apart from a few years when he was Ghana's director of tourism, Annan devoted his working life to the United Nations and other international agencies.
Having been in charge of UN human resources, its budget and then peacekeeping, the UN Security Council recommended Annan as secretary general in 1996. Mission impossibles soon came his way.
In 1998, Annan had to go to Baghdad to negotiate with Saddam after the Iraqi strongman threw out UN inspectors looking for signs of nuclear and chemical weapons.
He secured a deal to get inspectors back in, but it soon collapsed and US and British planes were bombing Iraq within months.
In 2004 he went to Khartoum to meet Sudan's strongman leader Bashir to press for an end to the campaign by Janjaweed militia against civilians in the Darfur region. Bashir relented, but the concessions were again short lived.
Credited with rebuilding the UN's reputation, he shared the Nobel Peace Prize with the United Nations in 2001.
And Annan has often proved his independence against the major powers.
He annoyed the United States and Britain when he said their 2003 invasion of Iraq was illegal because it was not supported by the UN Security Council.
Some commentators saw the 2005 investigation into Annan and his son over the UN oil-for-food corruption scandal in Iraq as a payback for his invasion comments.
Resisting calls for his resignation spearheaded by US right-wingers, Annan assumed responsibility after an independent enquiry panel cleared him of ethical lapses but documented evidence of corruption and management lapses.
Annan later said the investigations were the toughest part of his career.
He raised eyebrows again last year when he criticised the Western coalition on Libya. He said he feared their actions in helping to bring down Moamer Kadhafi had gone beyond the UN Security Council's mandate on Libya.
But Annan has won new praise for his role in ending Kenya's deadly turmoil in 2008 after widely criticised elections.
Annan came in as mediator, and through long weeks of negotiations convinced President Mwai Kibaki and opposition leader Raila Odinga to end their feud -- and fighting between their followers in which more than 1,300 people died.
"That was the kind of thing he could do because he was Kofi Annan," said James Traub, a commentator who has written a book about the former UN chief.
But there are differences between the past challenges and Bashar al-Assad in Syria, who has unleashed government forces on protesters leaving thousands dead in the past 11 months.
In Kenya, Annan had a special status as an African leader in an African setting, said Traub. "That is obviously not true in the Middle East."
"You have this guy Assad who has concluded that his only path to survival is to wade through an ocean of blood," added the writer.
"It is not clear what Annan or anybody else could say to him that would persuade him that his interests lay either in reconciliation or stopping the ruthless murder of his people."
Annan does have determination and what Traub calls a gift of persuading people like Saddam and Bashir.
"He is such a mild-mannered character," said Traub.
"People easily assume he is a weakling, whereas he is ego-less and strategically deploys his lack of ego to show deference for people who do not deserve deference, but may be persuaded through that deference to make concessions they might not make in a more confrontational setting."