In a rare instance of unity, leaders from around the world expressed their grief for the passing of former UN chief and Nobel peace laureate Kofi Annan, who died Saturday at the age of 80.

Described as a “guiding force for good” and “an outstanding human being,” a flood of tributes from around the world poured in for what many called a diplomatic rock star.

The Ghanaian national was a career diplomat who projected quiet charisma and was widely credited for raising the world body’s profile in global politics during his two terms as head of the UN from 1997 to 2006.

The first secretary general from sub-Saharan Africa, Annan led the United Nations through the divisive years of the Iraq war and was later accused of corruption in the oil-for-food scandal, one of the most trying times of his tenure.

“It is with immense sadness that the Annan family and the Kofi Annan Foundation announce that Kofi Annan, former Secretary General of the United Nations and Nobel Peace Laureate, passed away peacefully on Saturday 18th August after a short illness,” the foundation said in a statement.

“His wife Nane and their children Ama, Kojo and Nina were by his side during his last days.”

Annan, who lived not far from the UN European headquarters in Geneva, died in hospital in the German-speaking part of the country, Swiss news agency ATS reported.

Current UN chief Antonio Guterres described his predecessor as “a guiding force for good.”

“In many ways, Kofi Annan was the United Nations,” he said.

“He rose through the ranks to lead the organization into the new millennium with matchless dignity and determination.”

In a report in The Guardian, South Africa’s Archbishop Desmond Tutu described his death as a “devastating loss.” Annan was an “outstanding human being who represented our continent and the world with enormous graciousness‚ integrity and distinction,” said Tutu.

Others paying tribute included Tony Blair, once an adversary over the Iraq war.

According to The Guardian, the former British prime minister said: “He was a good friend whom I saw only weeks ago. Kofi Annan was a great diplomat, a true statesman and a wonderful colleague.”

Canadian Prime Minister Justin Trudeau said on Twitter: “Kofi Annan didn’t just talk about building a more just and peaceful world, he dedicated his life to doing it — and the world is a better place because of him. It’s now up to all of us to carry his work forward.

German Chancellor Angela Merkel told Associated Press Annan “inspired me and many others with his ideas, his firm convictions and, not least, his charisma.”

Russian President Vladimir Putin hailed his “wisdom and courage,” while French President Emmanuel Macron said on Twitter “we will never forget his calm and resolute gaze, nor the strength of his struggle.”

Former US president Barack Obama earlier said Annan “embodied the mission of the United Nations like few others.”

The UN said it would fly flags at half mast at all of its locations around the world through Tuesday.

In 2001, as the world was reeling from the September 11 attacks in the United States, Annan was awarded the Nobel Peace Prize jointly with the world body “for their work for a better organized and more peaceful world.”

Born in Kumasi, the capital city of Ghana’s Ashanti region, Annan devoted four decades of his working life to the UN and was the first chief to rise from within the organization’s ranks.

In 1993, he took over as peacekeeping chief — a position he held through two of the UN’s darkest chapters: the Rwandan genocide and the Bosnian war.

His tenure as UN chief was tarnished by a 2005 investigation of Annan and his son over the oil-for-food scandal, seen by some as payback for his comments that the 2003 US-led invasion of Iraq was “illegal.”

An inquiry cleared Annan of any serious wrongdoing, but found ethical and management lapses linked to his son Kojo’s ties with a Swiss firm that won lucrative contracts in the oil-for-food scheme.

Annan later admitted the scandal had sorely tested his mettle not only as secretary-general, but as a father.

Despite the lows, he left the post as one of the most popular UN leaders ever, and was considered a “diplomatic rock star” in international diplomatic circles.

After ending his second term as UN chief, he kept up his diplomatic work, taking high-profile mediation roles in Kenya and in Syria, and more recently leading an advisory commission in Myanmar on the crisis in Rakhine state.

He enjoyed some success in ending post-election turmoil in Kenya in 2007, and on Saturday the two main players in that crisis, former president Mwai Kibaki and his opposition rival Raila Odinga celebrated his efforts.