Profile: Nato secretary general Jens Stoltenberg

Nato's 13th secretary general, former Norwegian Prime Minister Jens Stoltenberg, looks an unlikely choice on several counts: an economist with no defence background, a social democrat who built up good relations with Russia, another Scandinavian hard on the heels of Anders Fogh Rasmussen.

Actually, the veteran social democrat presents a sharp contrast to his predecessor, the conservative former prime minister of Denmark, who could come over as strident and uncompromising about Russia.

There is likely to be concern among some east Europeans that he may be too accommodating towards Russia in the crisis over Ukraine.

Yet those fears may be premature.

He is a politician who will deal flexibly with facts on the ground, whether it is Nato's withdrawal from Afghanistan or conflict in eastern Europe, Harald Stanghelle, a leading Norwegian journalist, told BBC News.

Intriguingly, Mr Stoltenberg is also German Chancellor Angela Merkel's choice to lead the alliance, often regarded as the main instrument for keeping America in Europe.

Possibly nobody was as surprised as the Norwegians themselves at news that Jens Stoltenberg was taking Europe's top defence job.

Time was a Stoltenberg as Nato secretary general would have seemed natural - but that was Thorvald, father of Jens. The former defence and foreign minister, now 83, was tipped for the post back in the 1990s.

Following him into the Norwegian Labour Party, his economist son took a different path, becoming minister of industry and energy in 1993 before moving to finance in 1996.

In 2000, aged 40, he became prime minister for the first time. His Labour government lasted less than two years, suffering at the polls for its efforts to reform the welfare state.

When he returned to the post in 2005, it was as head of a coalition with the Socialist Left and Centre parties, which was returned again in 2009.

Born 16 March 1959 in Oslo (age 55), studied economics

Veteran member of Norway's Labour Party

Prime minister by 40, served three terms

Fluent English-speaker who grew up partly in Yugoslavia, where his father was Norwegian ambassador

Married to Ingrid Schulerud, with two grown-up children

The following year, Mr Stoltenberg signed an agreement with Russian President Dmitry Medvedev to resolve a decades-long border dispute in the oil- and gas-rich Barents Sea. Relations were improved still further in 2012 with the creation of a visa-free zone along their land border.

Under Mr Stoltenberg, Norway joined the US-led "War on Terror", contributing nearly 600 soldiers to the Nato-led peacekeeping force in Afghanistan, and suffering its share of casualties. All but 57, external were recently pulled out, ahead of Nato's full withdrawal this year.

Terrorism from a different quarter came in under the radar on 22 July 2011: Anders Behring Breivik's murderous one-man assault on his government and the Labour Party's youth wing.

Famously, the Norwegian prime minister said the response to the attack must be "more democracy, more openness".

A rather spirited gimmick of posing as cab driver to "hear voters' real concerns" could not save Jens Stoltenberg's government in 2013, when it lost to the centre-right, and the three-term prime minister was out of a job at the age of 54.

"News that he was to become the secretary general of Nato came as a surprise to the political elite and media world in Norway," says Stanghelle, external, political editor at Aftenposten, Norway's biggest daily.

"There had been a lot of discussion of Stoltenberg's future, at the UN perhaps, but there was no mention of Nato at all."

It appears that Mrs Merkel approached the former prime minister with the idea of heading Nato, an idea then endorsed by the Obama administration.

Despite the political differences between the Norwegian social democrat and the German conservative, the two had worked together well.

"She liked Stoltenberg quite a lot," Stefan Kornelius, external, foreign editor at a leading German daily, Sueddeutsche Zeitung, told BBC News. "He was sort of her favourite social democrat."

In one of his few recent pronouncements about Ukraine, Mr Stoltenberg said last week: "It is Russia that has chosen a more aggressive approach. The result is that we have not been able to follow up on our initial hope of a close and tight partnership."

But if any common ground is out there, the Norwegian politician is the man to find it, Stanghelle suggests.

"I don't think he has illusions about Russia but I think he will look for possibilities where Rasmussen may not have seen them. He is a consensus person, definitely, and a person who seeks compromises but he is also a very fact-orientated, skilful politician who works hard and looks for solutions.

"Rasmussen was a rash person who was direct in his way of speaking. It would be hard to find two people more different in their way of handling people."

It is never quite clear where the German chancellor wants to go with Nato, according to Kornelius, but her pick of Mr Stoltenberg serves several purposes for Germany, the EU's dominant state.

Despite her aversion to military issues, he argues, she is "enough of a realist not to expect the EU to take over substantially on defence".

"Now with Ukraine burning and the eastern members under pressure, she wants to bolster the alliance," he says.

At the same time, "by deciding on a social democrat from Scandinavia, she pre-empted a bit the other personnel decisions which had to be taken after this year's EU elections".

"The Nato job is part of a wider balance-of-interest game among European countries," in which conservatives predominate, according to Kornelius.

What the new head of the European Commission, conservative Brussels insider Jean-Claude Juncker, has in common with Mr Stoltenberg is that both are Merkel allies and both are consensus politicians.