Martti Ahtisaari, Finland's formidable former president who helped negotiate peace around the world after leaving domestic politics, died on Monday aged 86.

"It is with great sadness that we have received the news of the death of President Martti Ahtisaari," Finland's President Sauli Niinisto said in a statement. "He was president in times of change, who piloted Finland into a global EU era."

Ahtisaari, described by European Commission President Ursula von der Leyen as "a visionary" and "champion of peace," was instrumental in Finland's accession to the European Union, overseeing the country's referendum to join the EU during his first year of presidency.

He was an early advocate of Finland and Sweden joining NATO after Russia's invasion of Ukraine, which would occur shortly before his passing.

He would also build a reputation as a skilled peacemaker, setting up the Helsinki-based Crisis Management Initiative, a foundation aimed at preventing and resolving violent conflicts, and would become an influential voice onconflicts in the Middle East.

'Forever in the pages of Kosovo's history'

Ahtisaari was involved in the Northern Ireland peace process in the late 1990s, tasked with monitoring the IRA's disarmament process.

He played a role in Namibia's bid for independence in the 1980s and autonomy for the Aceh province of Indonesia in 2005, ending three decades of conflict that caused some 15,000 deaths.

Perhaps his most notable diplomatic achievement was in 1999 when he successfully negotiated, alongside Russia's Balkans envoy Viktor Chernomyrdin, an end to fighting in the Yugoslav province of Kosovo, leading to Serbia's withdrawal and ultimatelyKosovo's declaration of independence.

"President Ahtisaari committed all his life to peace, diplomacy, the goodness of humanity, and had an extraordinary influence on our present and the future," said Kosovo's President Vjosa Osmani. "He engraved the frame of our country, and his name will remain forever in the pages of the Republic of Kosovo's history."

From refugee to president

Born in 1937 in the eastern town of Viipuri, which is now the Russian town of Vyborg, Ahtisaari was forced to flee at the end of World War II after it was annexed by the Soviet Union. He would later say that his childhood experience of war and being a refugee "gave me sensitivity... perhaps that made me a peace negotiator."

After securing a teaching post in Pakistan in the early 1960s, he left a career as a primary school teacher behind in 1965 to embark on a career at Finland's Foreign Ministry.

He became a diplomat, first as an ambassador to Tanzania, then Zambia and Somalia before joining the United Nations in New York, becoming special representative for Namibia in 1978.

His work in Namibia, which led to the nation's independence from South Africa in 1990, was recognized by the Namibian government, which made him an honorary citizen.

After two decades away, he returned to Finland in 1991 to become Foreign Secretary for the Social Democratic Party and was elected president three years later, seen as a fresh face in the political landscape.

'Peace is a question of will'

After serving a single six-year term as president and declining to run again, Ahtisaari's lifetime of diplomatic work was rewarded with the Nobel Peace Prize in 2008.

Upon accepting the award, he told the Nobel celebration: "Peace is a question of will. All conflicts can be settled, and there are no excuses for allowing them to become eternal."

In 2017, he stepped down as chairman of his foundation and continued to work as an advisor until 2021, when his Alzheimer's condition worsened.

His replacement as chairman, former Finnish Prime Minister Alexander Stubb, who is now running for president of Finland, reacted to his precessor's death on social media, writing: "perhaps now more than ever, the world needs people like him."

Ahtisaari, who will receive a state funeral, is survived by his wife Eeva and their adult son Markko.

mds/msh (AFP, reuters, AP)