Former United Nations Secretary-General Kofi Annan has died at the age of 80 of an unspecified illness.
Annan died in the early hours of August 18 in a hospital in Bern, Switzerland.
"It is with immense sadness that the Annan family and the Kofi Annan Foundation announce that Kofi Annan…passed away peacefully…after a short illness," the foundation said in a statement.
Current UN head Antonio Guterres called Annan "a guiding force for good."
"In many ways, Kofi Annan was the United Nations," he added.
The president of Annan's native Ghana, Nana Akufo-Addo, called Annan "one of our greatest compatriots" and ordered flags lowered to half-mast for one week.
World leaders paid tribute to Annan, who became the UN's first black African secretary-general in 1997 and served two terms until 2006.
German Chancellor Angela Merkel said Annan "inspired me and many others with his ideas, his firm convictions and, not least, his charisma."
French President Emmanuel Macron said that "we will never forget his calm and resolute look, nor his strength in battles," while British Prime Minister Theresa May said Annan "made a huge contribution to making the world he has left a better place than the one he was born into."
Russian President Vladimir Putin said he "sincerely admired his wisdom and courage as well as his ability to make balanced decisions even under the most dire and critical circumstances."
Former U.S. President Barack Obama said Annan "embodied the mission of the United Nations like few others."
U.S. Secretary of State Mike Pompeo said the former UN chief "spent his life advocating for peace and human dignity during his long career at the United Nations."
"Even after leaving his post as secretary-general, he embodied the mission of the United Nations, by sowing the seeds of peace as Chair of The Elders, an independent group of global leaders committed to advancing the cause of peace and promoting human rights around the world," Pompeo added.
Annan spent virtually his entire career at the United Nations. As head of UN peacekeeping operations in the 1990s, Annan was harshly criticized for the UN's failure to stop the Rwandan genocide in 1994 and to prevent the massacre of more than 8,000 Bosnian Muslim men and boys at Srebrenica in 1995.
He became the organization's first black African secretary-general in 1997 and served two terms until 2006. Although the UN experienced turbulence and scandals during Annan's tenure, his personal style and charisma were seen as key factors enabling the body to weather them.
Annan and the United Nations were jointly awarded the Nobel Peace Prize in 2001 "for their work for a better organized and more peaceful world."
It was widely accepted that Annan left the UN a stronger organization with a clearer agenda for peacekeeping, promoting human rights and development, and combating poverty.
Guterres noted on August 18 that Annan led "the organization into the new millennium with matchless dignity and determination."
In an interview in 2013, Annan said his "darkest moment" was his inability to stop the U.S.-led war against Iraq in 2003.
"I worked very hard," he said. "I was working the phone, talking to leaders around the world. The U.S. did not have the support in the Security Council. So they decided to go without the council. But I think the council was right in not sanctioning the war."