When Martti Ahtisaari, the sturdy Finn who successfully negotiated agreements to end conflicts in Asia, Africa and Europe, accepts the 2008 Nobel Peace Prize in Oslo on December 10, it will be the fourteenth Peace Prize to go to a person or group involved in United Nations work.

Inevitably, in an organization of 192 member nations with differing opinions on war and peace, there is controversy. In Ahtisaari’s case, critics are focused on his most recent assignment, Kosovo, and whether he acquiesced too readily in the Kosovars’ demand for independence from Serbia, which rankled in Moscow. The Nobel committee took a longer view of his career.

Kofi Annan, who as UN secretary general sent Ahtisaari on some of his most challenging missions, including Kosovo, describes him as “the only man I know who has made peace on three continents.” In a telephone interview from his office in Geneva, Annan acknowledged that not everyone supports the outcome in Kosovo, but he applauded the Nobel award. “I don’t think the prize could have gone to a better person than Martti, who has been engaged in peace processes since the late ’70s,” he said.

For more than three decades, Ahtisaari has ranked high among a small band of global troubleshooters for the UN, none of them American. They include Lakhdar Brahimi from Algeria; Alvaro de Soto of Peru; the late Sergio Vieira de Mello, a Brazilian; and the redoubtable Margaret Anstee of Britain, one of the few women in the field (she wrote about her eventful and sometimes zany life in the 2004 book Never Learn to Type).

Ahtisaari, a 71-year-old former schoolteacher, possesses a formidable demeanor: tall, solidly built and not given to emotion. His colleagues say this matches a character of strong conviction, perseverance in negotiations, a penchant for blunt talking and, when needed, undiplomatic language and some table-pounding.

“Martti has deep political instincts and is guided by rock-solid moral principles,” said Frederic Eckhard, who was a top aide to Ahtisaari in Namibia and the Balkans. Ahtisaari never masked his opinions in reports to the UN. In 1991, looking at the human fallout of the war to liberate Kuwait, he accused the United States of bombing Iraq into a “pre-industrial age.” In 2003 he blasted the UN for the “bureaucratic inertia” that led to security lapses at UN headquarters in Baghdad, where twenty-two people were killed (including Vieira de Mello) when the building was hit by a truck bomb. “Whatever people said, it could have been prevented,” Eckhard is quoted as saying in his forthcoming book Kofi Annan, whom he served as spokesman when Annan was head of UN peacekeeping and later secretary general.

Ahtisaari, who served as Finland’s ambassador to several African countries in the 1970s (and later was president of Finland from 1994 to 2000), has said that the most important work of his life was done in Namibia, a former German colony known as South West Africa, where apartheid South Africa claimed jurisdiction in defiance of UN resolutions. “Martti served so long as a diplomat in Africa that I believe he planted roots there,” said Eckhard.

The rebel South West Africa Peoples Organization (SWAPO), at war against the South Africans, was recognized in the UN General Assembly as the “sole legitimate representative” of the Namibian people. From 1977 to 1990, Ahtisaari was involved in efforts to make independence a reality.

The controversial American policy of “constructive engagement” with South Africa, directed by Chester Crocker, assistant secretary of state for African affairs in the Reagan administration, eventually helped start talks involving South Africa, Angola, the United States and Russia. An agreement under which Cuban troops were to leave Angola and South Africans would give up Namibia and cease support for the UNITA rebels fighting the Angolan government, opened the way to independence, and Ahtisaari’s political team, backed by peacekeepers and civilian police, led the transition to civilian rule. In 1990 the SWAPO leader, Sam Nujoma, was elected Namibia’s president.

In the Balkans, Ahtisaari was given the task in 1992-93 of dividing Bosnia into Serb, Croat and Muslim areas as part of a peace plan devised by former US secretary of state Cyrus Vance and his British counterpart, David Owen. Ahtisaari’s proposal was rejected by the Clinton administration because, Eckhard said, it gave 51 percent of the territory to Bosnian Serbs and “Clinton had campaigned on a ‘Get tough with the Serbs’ platform.” The Vance-Owen plan died, but, Eckhard added, the Serbs got even more land in the 1995 Dayton accords negotiated by Clinton’s envoy, Richard Holbrooke.

After his term as president of Finland ended in 2000, Ahtisaari became board chairman of the International Crisis Group, an independent analysis and advocacy organization based in Brussels.

By 2005 he was in Southeast Asia. In the wake of the devastating 2004 Indian Ocean tsunami, he negotiated a political settlement of the separatist struggle in the Aceh region of Indonesian Sumatra, the epicenter of tsunami damage. For more than a century the Acehnese had resisted integration under both Dutch colonial rulers and independent Indonesia.

Annan said that after he persuaded Indonesia’s president, Susilo Bambang Yudhoyono (who had earlier worked with the UN as a peacekeeping commander in Croatia and on the independence of East Timor), to open talks on Aceh’s future, Ahtisaari was able to broker a deal under which Indonesian troops were withdrawn and separatists disarmed and moved into leadership roles in local politics.

Kosovo was different. The Kosovars would settle for nothing less than a complete break with Serbia. In 2005 Annan assigned Ahtisaari to this overwhelmingly Muslim, ethnic Albanian province, which saw a chance to snatch independence out of the breakup of Yugoslavia. It was an ugly conflict with atrocities on both sides, into which the United States entered with the bombing of Serbia in 1999, acting outside the UN Security Council.

After months of talks with Kosovars and Serbs in 2005-06, Ahtisaari presented a plan in early 2007, under the new UN Secretary General Ban Ki-moon, that amounted to a blueprint for “supervised independence.” For the Russians, supporters of the Serbs, that was unacceptable. The Kosovars declared independence in February of this year. Fifty-two countries have since recognized Kosovo’s independence, the majority in Europe and the Americas, led by the United States. Islamic nations are now joining the list, with the United Arab Emirates and Malaysia the most recent and Bangladesh in the offing.

Criticism, not only from Russia but also from a number of developing nations, was immediate. “Martti went one step farther than necessary,” a diplomat from a country not involved in the dispute said of Ahtisaari’s blueprint. “Washington, London and Brussels planned this outcome, and he rubber-stamped it. There is a groundswell of opinion against him.”

The rebuff to Russia and Serbia is often mentioned as a contributing factor in Moscow’s large-scale use of force in border regions of Georgia in August after a Georgian attack on its breakaway region of South Ossetia, which Russia then declared independent along with Abkhazia.

Annan said that working between two parties resistant to compromise, Ahtisaari did what he could to try to help resolve a very difficult problem in the still restive Balkans. Discord persists. The contrast with the afterglow of Namibia could not have been greater.

“In Namibia they couldn’t have been happier with him,” Annan said. “I used to tease him that the people were so grateful that they named many children after him. After he left there were a lot of little Marttis running all over the place. He said, ‘Kofi, I had nothing to do with that.’ ”