Up until the election campaign, his political reputation had been unsullied. But, as he sought the presidency on behalf of the Social Democratic Party, Mr. Ahtisaari faced — and denied — critics’ assertions that he had struggled with alcohol abuse and had taken a double salary from the Finnish foreign ministry and the United Nations for his mediation efforts in Bosnia.
Even as president, he continued as a peacemaker, negotiating to end fighting in Kosovo in 1999.
After he stepped down as president, Mr. Ahtisaari he founded the nonprofit Crisis Management Initiative, which helped promote peace in the Indonesian province of Aceh, where, for 29 years, insurgents from the Free Aceh Movement fought for independence from the government in Jakarta.
Under a peace treaty signed in Helsinki, the Finnish capital, in 2005, the rebels agreed to drop their demands for full independence in the province, which has vast reserves of oil, natural gas, timber and minerals, and settle for broad autonomy in return for the withdrawal of some Indonesian security forces.
While previous peace efforts had failed, the overwhelming impetus for a settlement came finally from an unlikely quarter when the tsunami of December 2004 devastated Aceh province, killing 170,000 people, making 500,000 homeless and prompting the combatants to return to negotiations.
Despite his somewhat stern appearance, Mr. Ahtisaari was known for some idiosyncratic behavior. Such was his love of his land’s favored form of relaxation, for instance, that he sometimes invited aides to continue their deliberations in the sauna.
Johanna Lemola contributed reporting.