Kofi Annan, the former UN secretary-general who won the Nobel Peace Prize for humanitarian work, has died aged 80 after a short illness, international diplomats say.
Annan was the first black African to take up the role of the world's top diplomat, serving two terms from 1997 to 2006.
He later served as the UN special envoy for Syria, leading efforts to find a peaceful solution to the conflict.
Annan's wife Nane and their children Ama, Kojo and Nina were by his side during his last days, Kofi Annan Foundation said in a Facebook statement announcing his death on Saturday.
"Kofi Annan was a global statesman and a deeply committed internationalist who fought throughout his life for a fairer and more peaceful world. During his distinguished career and leadership of the United Nations he was an ardent champion of peace, sustainable development, human rights and the rule of law."
The diplomat, who was originally from Ghana, had been living in Geneva for several years before his death.
He was awarded the Nobel Peace Prize in 2001 for helping to revitalise the international body, during a period that coincided with the Iraq war and the HIV/Aids pandemic.
Kofi Annan described his greatest achievement as the Millennium Development Goals which — for the first time — set global targets on issues such as poverty and child mortality.
However, Mr Annan was not immune to criticism. His critics blamed him for the UN's failure to halt the genocide in Rwanda in the 1990s when he was head of the organisation's peacekeeping operations.
Later, after the US-led invasion of Iraq, he and his son were accused of being involved in the "oil for food scandal" that led some to call for his resignation, though he was later exonerated.
In an interview with the BBC's HardTalk to mark his 80th birthday in April, Mr Annan acknowledged the UN's shortcomings, saying it "can be improved, it is not perfect but if it didn't exist you would have to create it".
"I am a stubborn optimist, I was born an optimist and will remain an optimist," he added.
Current UN chief Antonio Guterres has been leading the tributes to his predecessor, describing Mr Annan as "a guiding force for good".
"In many ways, Kofi Annan was the United Nations. He rose through the ranks to lead the organisation into the new millennium with matchless dignity and determination," he said in a statement.
Annan was key in bringing peace to Kenya following the disputed 2007/08 General Election that quickly spiralled into violence, leaving many displaced and hundreds killed.
It was Annan who brought retired President Mwai Kibaki and Orange Democratic Movement leader Raila Odinga to the negotiating table.
He brokered the peace accord that formed the Grand Coalition government, ending months of violence over the disputed election results.
Mr Odinga on Saturday in a phone call to Citizen TV said Annan's death is a big a loss for Africa.