Kofi Annan of Ghana, whose popular and influential reign as secretary general of the United Nations was marred by White House anger at his opposition to the American invasion of Iraq in the early 2000s, died Aug. 18 at a hospital in Bern, Switzerland. He was 80.

The death was announced by the Annan family and the Kofi Annan Foundation. The cause was not immediately disclosed.

Current U.N. Secretary General António Guterres called Mr. Annan “a guiding force for good,” and added: “He provided people everywhere with a space for dialogue, a place for problem-solving and a path to a better world.”

Mr. Annan, who pronounced his last name ANN-un to rhyme with “cannon,” shared the 2001 Nobel Peace Prize with the international body he led from 1997 to 2006. He owed his original triumph and his later turmoil to tense relations with the United States, but in some ways, he was an accidental secretary general.

His predecessor, Egyptian diplomat and minister Boutros Boutros-Ghali, was vilified by conservative American politicians for supposedly leading the United States into disastrous overseas adventures. The Clinton White House was no more enamored of Boutros-Ghali’s leadership and imperious personal style and clashed with the secretary general over his reluctance to bomb the Serbs during the conflict in Bosnia.

The personal enmity between the secretary general and Madeleine Albright, then serving as U.S. ambassador to the United Nations, had grown so bitter that she vetoed Boutros-Ghali’s bid for a second term in 1996 even though he had the support of all 14 other members of the Security Council.

Albright assuaged African member countries by sponsoring Mr. Annan, a well-liked U.N. insider who had joined the organization in 1962 and rose through the bureaucracy mainly by handling personnel and budget matters.

Mr. Annan became the seventh secretary general and the first black African to hold the job. He did not fit the stereotype of the haughty and secretive international civil servant.

He tried to answer all questions of reporters and ambassadors with disarming frankness. He published long reports, chock full of classified cables, that detailed the United Nations’ mistakes in dealing with the massacre in Srebrenica during the Balkans war and Rwanda in the 1990s — a period when he was chief of peacekeeping.

In 1995, Mr. Annan oversaw the transfer of U.N. peacekeeping forces in Bosnia to a NATO-led force after years of devastating ethnically driven conflict. Mr. Annan’s comments at the time reflected the anguish felt by many at the United Nations over being unable to end that war.

“In looking back we shall all record how we responded to the escalating horrors of the last four years,” he said. “And as we do so, there are questions that each of us will have to answer. What did I do? Could I have done more? And could it have made a difference? Did I let my prejudice, my indifference and my fear overwhelm my reason? And how would I react next time?”

His most important legacy as secretary general was his rejection of the long-standing notion that the United Nations could not interfere in the internal affairs of a member country.

He finally persuaded the United Nations that a government’s suppression of its own people threatened international stability, making it a proper issue for the Security Council. This doctrine eventually led to the U.N. resolution that authorized the NATO bombing that helped end the dictatorial regime of Moammar Gaddafi in Libya in 2011.

Mr. Annan tried to make the position of secretary general more familiar to Americans. He threw out the first pitch at a 1999 World Series game in Yankee Stadium. He appeared on the children’s television show “Sesame Street,” leading the squabbling Muppets in a U.N. group hug.

He and his wife, Nane, danced at so many dinners and parties that William H. Luers, a veteran U.S. diplomat and a past president of the Metropolitan Museum of Art, once called him a “social star of New York society.”

Mr. Annan’s first celebrated term as secretary general was capped by the Nobel Peace Prize. “In an organization that can hardly become more than its members permit, he has made clear that sovereignty can not be a shield behind which member states conceal their violations,” the Nobel committee wrote.

The United Nations works best when the secretary general and the U.S. president agree on most major issues. For that reason, Mr. Annan had a bruising second term as he pushed back against President George W. Bush’s growing determination to invade Iraq for supposedly harboring weapons of mass destruction.

“He had the bad luck to be secretary general when Washington was run by a band of ideologues,” Brian Urquhart, a former undersecretary general who is the dean of U.N. commentators, said of Mr. Annan in an interview. “If the United States had been on his side, he would have been regarded as in the class of Dag Hammar­skjold,” the Swedish diplomat widely regarded as the U.N.’s greatest secretary general.

Mr. Annan became a continual irritant to the Americans. He eliminated an easy excuse for war by persuading the Iraqis to allow U.N. inspectors back in to search for weapons of mass destruction. He emboldened the ambassadors from Chile and Mexico to withhold support for an American resolution authorizing an invasion.

When U.S. forces invaded Iraq in March 2003, Mr. Annan deplored the American failure “to solve this problem by a collective decision.”

Afterward, Mr. Annan infuriated the White House by telling a BBC reporter that the invasion was “illegal” and by sending a letter to Bush and British Prime Minister Tony Blair imploring them not to attack the Sunni Muslim city of Fallujah.

Bush aides thought the secretary general was trying to embarrass the president during his 2004 reelection campaign. Randy Scheunemann, a Republican foreign policy specialist, told the BBC that Mr. Annan’s labeling of the war as illegal was “outrageous” and “reeks of political interference.”

Mr. Annan wanted to keep channels open so that the United Nations could help the people of Iraq after the invasion. This would come to haunt the secretary general when a suicide bomber blew up U.N. headquarters in Baghdad in August 2003, killing his friend and troubleshooter Sergio Vieira de Mello of Brazil and 21 other U.N. officials.

“You send in some of your best people, who are friends,” Mr. Annan said in an interview, “and they get killed for trying to sort out the aftermath of the war you didn’t support; you can imagine my discouragement and melancholy. It was tough.”

Mr. Annan was buffeted a year or so after the invasion by a conservative campaign against him over what was called the “oil-for-food” scandal. Under the program, implemented in 1996 while Iraq was under sanctions before the invasion, Saddam Hussein was allowed to sell some oil to buy food for his people.

A commission headed by former Federal Reserve chairman Paul A. Volcker found that Hussein had profited illegally by almost $2 billion under the program from overpayments for oil and kickbacks for food.

Outside the oil-for-food corruption, according to the Volcker commission, the Iraqi regime had earned even more illegal profits — almost $11 billion — by smuggling oil to Turkey, Jordan and other countries. Mr. Annan told reporters that most of these illegal sales had been allowed by American and British officials who “decided to close their eyes to smuggling to Turkey and Jordan because they were allies.”

This U.S.-British complicity in the illegal commerce — an open secret for years — was confirmed later by Kenneth Pollack, who monitored Iraqi oil sales for the Clinton White House.

The Volcker commission did not accuse Mr. Annan of making a single penny from the oil-for-food transactions. But it accused him of a failure of management for not preventing the corruption.

Moreover, the commission found that Mr. Annan’s son, Kojo, was on the secret payroll of a Swiss company trying to do business under the oil-for-food program. The secretary general was cleared of trying to do anything to favor the Swiss firm, but the son’s foolishness, as Mr. Annan put it, “caused me lots of grief.”

Mr. Annan was still venerated throughout the rest of the world, and after retiring from the United Nations in 2006 he soon took on a role in the mold of former South African president Nelson Mandela, as a wise, noble elder trying to mediate a host of conflicts in his native Africa.

Kofi Atta Annan was born with a twin sister on April 8, 1938, in Kumasi, Ghana — in what was then the British colony of the Gold Coast. His father was a senior buyer of cocoa for the Anglo Dutch corporation Unilever. He named his son in the Ghanaian Akan language: Kofi means “born on Friday” and Atta means “twin.”

After attending schools in the Gold Coast, Mr. Annan won a Ford Foundation scholarship to Macalester College in St. Paul, Minn. After receiving a bachelor’s degree in economics in 1961, he found work as a junior administrative and budget officer with the U.N. World Health Organization in Geneva. He received a master’s degree in management from the Massachusetts Institute of Technology in 1972.

Mr. Annan began to attract wider notice at the start of the Persian Gulf War in 1990. On a special mission to Baghdad as chief of personnel, he helped persuade the Iraqis to release 900 U.N. employees and dependents held as hostages. He also organized an airlift of hundreds of thousands of Asian workers back to their original homes.

Boutros-Ghali pulled Mr. Annan out of the United Nations’ bureaucratic ranks in 1992, naming him deputy chief of peacekeeping, the most dramatic work done by the United Nations. The next year, Mr. Annan was promoted to chief of peacekeeping with the rank of undersecretary general, the highest in the U.N. civil service. Mr. Annan presided over a record expansion of peacekeeping to 75,000 troops in 19 missions.

In his new role, Mr. Annan drew strong criticism from some journalists and activists for failing to sound the alarm about the threat of impending genocide in Rwanda. He and his aides worked behind the scenes to prevent the widespread killing in Rwanda, but they said the forces of ethnic hatred were too strong to temper. When the massacres erupted in the mid-1990s, the U.N. Security Council, led by the United States, did little to stop them; hundreds of thousands were killed.

Mr. Annan’s first marriage, to Nigerian-born Titilola Alakija, ended in divorce. In 1984, he married Nane Lagergren, a Swedish lawyer and jurist. Her uncle was Raoul Wallenberg, the Swedish diplomat who saved the lives of thousands of Hungarian Jews during World War II and disappeared mysteriously in 1945 while in the custody of the Soviet army.

In retirement, Mr. Annan lived in Switzerland. Besides his wife, survivors include two children from his first marriage and a stepdaughter. A complete list of survivors could not be confirmed.

Though soft-spoken, Mr. Annan was often eloquent. He received the Nobel Peace Prize in Oslo just three months after the Sept. 11, 2001, attacks, and his acceptance speech took note of that terrible day.

“Ladies and gentlemen,” he said, “we have entered the third millennium through a gate of fire. If today, after the horror of 11 September, we see better, and we see further — we will realize that humanity is indivisible. New threats make no distinctions between races, nations or regions. . . . A deeper awareness of the bonds that bind us all — in pain as in prosperity — has gripped young and old.”

Stanley Meisler, a veteran foreign correspondent, was the author of "Kofi Annan: A Man of Peace in a World of War" and of "United Nations: A History.'' He died in 2016.‍