Jens Stoltenberg prepares to face Putin for another year at the helm of NATO

BRUSSELS—Five months ago, Jens Stoltenberg was preparing for a comfortable job in Norway, running one of the world’s most stable central banks and wealthiest sovereign wealth funds. Instead, he is now flirting with risks as extreme as nuclear war after signing on for an exceptional fourth term as NATO secretary general.

Mr Stoltenberg, a former Norwegian prime minister, began leading the North Atlantic Treaty Organization in 2014, months after Russia seized the Crimean peninsula from Ukraine and fomented a rebellion in the east from the country. Since then, he has overseen the biggest transformation and expansion of the Western military alliance since the Cold War.