With his mild manner, sober suits, and scholarly spectacles, Martti Ahtisaari might seem an unlikely figure to mediate peace with Aceh rebels, Namibian freedom fighters, or sectarian Iraqis.

But the former primary school teacher who became Finland’s president in the 1990s - and on Friday won the Nobel Peace Prize - is widely known as a skilled and dogged negotiator who honed his skills as a long serving Finnish diplomat and later as a UN undersecretary-general.

Ahtisaari has tried to settle conflicts as diverse as Namibia’s war of independence and the civil war between Iraq’s opposing Shia and Sunni factions. But he remains best-known for helping end in 2005 one of modern history’s longest-lasting conflicts between Aceh rebels and the Indonesian government.

After the 1990 Gulf War, he directed the UN’s approach to Iraq. His moderate policies, including advocating the lifting of international embargoes on food and medical supplies, are believed to have cost him Washington’s support in the election for UN secretary-general.

“Martti is a brilliant negotiator and mediator, with a tremendously effective personal style that combines charm and good humour with an iron determination,’’ said Gareth Evans, a former Australian foreign minister who heads the Brussels-based International Crisis Group.

Ahtisaari’s most controversial peacemaking effort came last year, when he failed to overcome Serbia’s refusal to relinquish Kosovo, a southern province which had become an international protectorate after a Nato bombing campaign against Serb forces in 1999.

The territory of two million people - 90 per cent of them ethnic Albanians - unilaterally declared independence last February after the yearlong talks failed to deliver an accord. The unsuccessful effort to find common ground between Belgrade and Kosovo’s capital of Pristina handed the veteran negotiator a string of headaches and disappointments. In a February 2007 interview with The Associated Press in Vienna, Austria, Ahtisaari struggled to contain his gloom.

“I could give you a list of a thousand things that could go wrong,’’ he said - presciently as it turned out.

After many years of living abroad and not being involved in domestic politics, Finland’s Social Democratic Party persuaded Ahtisaari to run as its presidential candidate in 1994.

Widely seen as a breath of fresh air, he won the election but never appeared truly comfortable in his role as head of state.

He also often appeared irritated by criticism in the domestic media, and declined to run for a second term saying he wanted to focus on peace efforts and helping to solve international crises.

In 2000, Ahtisaari set up the Crisis Management Initiative, his own non-governmental organization that has since been engaged in a number of discreet peace initiatives around the world.

During his time as a peacemaker in Northern Ireland in 2000, Ahtisaari sought to reconcile competing demands for Irish Republican Army disarmament by agreeing to visit IRA arms dumps in secret. Ahtisaari once light heartedly summed up his attitude toward peacemaking, saying it was like fishing for salmon.

“It’s such a good fish that it’s worthwhile trying everything to get it even if you don’t succeed in the end,’’ he told The Associated Press in an interview in 2005.``Incidentally, I’ve never caught a salmon in my life.’’