Mr Ahtisaari had been a favourite to win the Nobel peace prize for years
Former Finnish President Martti Ahtisaari is a veteran negotiator who has played a leading role in peace deals in several regions of the world.
Over a long career, Mr Ahtisaari has earned a reputation as a diplomat able to handle the thorniest of problems.
He played a particularly important role in the 2005 peace accord between Indonesia and rebels in Aceh province.
The deal ended a three-decade conflict in which 15,000 people died, helping win him the 2008 Nobel Peace Prize.
The citation said his efforts had contributed to a more peaceful world and to "fraternity between nations".
In early October, Mr Ahtisaari also received Unesco's Felix Houphouet-Boigny Peace Prize for his lifetime contribution to world peace.
Born in 1937, Mr Ahtisaari trained as a primary school teacher before joining Finland's Foreign Ministry in 1965.
He spent 20 years abroad, first as ambassador to Tanzania and then to the United Nations in New York.
Mr Ahtisaari played a significant part in negotiations that led to the independence of Namibia from South African rule in 1990.
It remains his proudest achievement. He says it was "absolutely the most important because it took such a long time".
His efforts helped usher in peace to Aceh province
In 1993, he was appointed special adviser to the UN secretary-general on former Yugoslavia, but a year later was elected president of Finland on a social democrat ticket.
Acting for the EU, in 1999 Mr Ahtisaari helped persuade then Yugoslav President Slobodan Milosevic to accept Nato's terms for ending the war in Kosovo.
He decided to bow out of Finnish politics in 2000, setting up the Crisis Management Initiative which works to promote peace and crisis resolution. He remains its chairman.
His appointments include that of UN Special Envoy for the Horn of Africa, and Personal Envoy of the OSCE for Central Asia.
In 2000, he drafted a report on the human rights and political situation in Austria after the far-right Freedom Party's entry into a coalition government.
The next year, he served as an independent arms inspector in Northern Ireland.
He has maintained strong links with the UN, heading an investigation into its security after a devastating car bomb attack on its Baghdad headquarters in August 2003.
In 2005, he again returned to the international spotlight when he organised talks between Indonesia's government and the Free Aceh Movement, who eventually signed a peace deal to end a 30-year uprising.
In the same year, he led intense mediation efforts to clinch a joint agreement between Serbia and Kosovo, although the push failed after Pristina unilaterally declared independence.
He is married with one son.