ACCRA, Ghana — Kofi Annan, a charismatic global diplomat and the first black African to become United Nations secretary-general who led the world body through one of its most turbulent periods, died early Saturday at age 80.

Tributes flowed in from around the world after his foundation announced his death in the Swiss capital, Bern, after a short and unspecified illness. The statement remembered the Nobel Peace Prize winner as “radiating genuine kindness, warmth and brilliance in all he did.”

He died “peacefully in his sleep,” the president of Ghana, where Annan was born, said after speaking to his wife.

At U.N. headquarters in New York, a bouquet of flowers was placed under Annan’s portrait. Reflecting the widespread regard that won him a groundbreaking uncontested election to a second term, leaders from Russia, India, Israel, France and elsewhere expressed condolences for a man Bill Gates called “one of the great peacemakers of our time.”

Annan spent virtually his entire career as an administrator in the United Nations. His aristocratic style, cool-tempered elegance and political savvy helped guide his ascent to become its seventh secretary-general, and the first hired from within. His two terms were from Jan. 1, 1997, to Dec. 31, 2006, capped nearly midway when he and the U.N. were jointly awarded the Nobel Peace Prize in 2001.

During his tenure, Annan presided over some of the worst failures and scandals at the world body. Challenges from the outset forced him to spend much of his time struggling to restore its tarnished reputation.

His enduring moral prestige remained largely undented, however, both through charm and by virtue of having negotiated with most of the powers in the world.

When he departed from the United Nations, he left behind a global organization far more aggressively engaged in peacekeeping and fighting poverty, setting the framework for its 21st-century response to mass atrocities and its emphasis on human rights and development.

“In many ways, Kofi Annan was the United Nations,” current U.N. Secretary-General Antonio Guterres said. “He rose through the ranks to lead the organization into the new millennium with matchless dignity and determination.”

Even out of office, Annan never completely left the U.N. orbit. He returned in special roles, including as the U.N.-Arab League’s special envoy to Syria in 2012. He remained a powerful advocate for global causes through his eponymous foundation.

Annan took on the top U.N. post six years after the collapse of the Soviet Union and presided during a decade when the world united against terrorism after the Sept. 11 attacks — then divided deeply over the U.S.-led war against Iraq. The U.S. relationship tested him as a world diplomatic leader.

“I think that my darkest moment was the Iraq war, and the fact that we could not stop it,” Annan said in a February 2013 interview with TIME magazine to mark the publication of his memoir, “Interventions: A Life in War and Peace.”

“I worked very hard — I was working the phone, talking to leaders around the world. The U.S. did not have the support in the Security Council,” Annan recalled in the videotaped interview posted on his foundation’s website.

“So they decided to go without the council. But I think the council was right in not sanctioning the war,” he said. “Could you imagine if the U.N. had endorsed the war in Iraq, what our reputation would be like? Although at that point, President (George W.) Bush said the U.N. was headed toward irrelevance, because we had not supported the war. But now we know better.”

Despite his well-honed diplomatic skills, Annan was never afraid to speak candidly. That didn’t always win him fans, particularly in the case of Bush’s administration, with whom Annan’s camp spent much time bickering. Much of his second term was spent at odds with the United States, the U.N.’s biggest contributor, as he tried to lean on it to pay almost $2 billion in arrears.

At the end of his Nobel acceptance speech Annan reminded the world why such pressure is necessary. “Beneath the surface of states and nations, ideas and language, lies the fate of individual human beings in need,” he said. “Answering their needs will be the mission of the United Nations in the century to come.”