SEOUL • North Korean leader Kim Jong Un ranks among the world's youngest heads of state, but has some of its most powerful weapons at his disposal.
Yesterday's test of what appeared to be a powerful, full- fledged thermonuclear bomb marked yet another watershed in Mr Kim's relentless drive as leader to turn the North into a credible - and feared - nuclear-armed state.
In the process, he has simply shrugged off international warnings and economic sanctions, as well as bellicose threats from United States President Donald Trump of possible military strikes if he persists.
When he took over from his late father Kim Jong Il nearly six years ago, he was in his late 20s, considered untested, vulnerable and likely to be manipulated by senior figures.
But he swiftly proved his mettle in dealing harshly - sometimes brutally - with any sign of dissent, even at the highest levels, while maintaining an aggressively provocative stance with the global community.
In 2013, he had influential uncle and mentor Jang Song Thaek executed for treason, and he was also believed to be behind the dramatic assassination of his exiled half-brother Kim Jong Nam in Malaysia earlier this year.
He has even shown he is willing to alienate the North's sole major ally China with his unstinting efforts to advance the country's nuclear and missile programmes in the face of Beijing's clear opposition - and has still not visited his neighbour to pay his respects to leader Xi Jinping.
After his father's death, Mr Kim was expected to initially rely on a coterie of powerful aides. But that expected tutelage was short-lived as he started to remove any potential challenges to his authority by executing Mr Jang. Other purges of high-ranking officials followed and, last year, he had himself appointed as chairman of a new supreme governing commission, underlining his absolute control over every aspect of state policy.
Mr Kim was born to his father's third wife, Japan-born ethnic-Korean dancer Ko Yong Hi, who is believed to have died of breast cancer in 2004.
He was sent to school in Switzerland, where he was looked after by his maternal aunt Ko Yong Suk and her husband.
In an interview with The Washington Post, Ms Ko - who defected to the US in 1998 - described Mr Kim as short-tempered and lacking in tolerance.
Mr Kim knew from his eighth birthday that he would become North Korea's leader, but he entered the public eye only in 2008 when his father suffered a stroke and Pyongyang revved up plans for the nation's second dynastic succession.
Despite his inexperience, he has shown himself adept at the high-risk strategy of diplomatic brinkmanship practised by his father and grandfather - founding leader Kim Il Sung - engineering a series of crises and then sharply driving up the stakes and challenging the international community to respond.
Though he has been in power for nearly six years, Mr Kim remains something of an unknown quantity on the world stage, having never travelled overseas in any official capacity.