Four years into his tenure, North Korea`s young leader Kim Jong Un has proven unpredictable and truculent, not only for the United States and South Korea but for his closest ally, China, defying it by conducting nuclear tests, the latest this week.
Mocked early on in his rule for his youth and girth, the third-generation dictator has thwarted the direst predictions of chaos and even collapse.
While many North Koreans remain desperately poor, a flourishing grey-market economy is improving the lives of ordinary people, delivering on one of Kim`s main policy pledges, even as the country is more isolated than ever.
North Korea said this week it successfully conducted a hydrogen bomb test, although the United States and other governments doubt the device was as advanced as claimed.
Still, the test will help Kim further consolidate his power by burnishing his image as a powerful leader and satisfying the government`s hard-line military constituency, at the beginning of a big year for North Korea.
In May it will hold just the seventh meeting of its 70-year-old ruling party, the first since 1980, when Kim`s father, Kim Jong Il, was himself being groomed as future leader under his father, the country`s founder, Kim Il Sung.
The nuclear test sets the stage for the congress.
"To him, the idea is, if you`re going to have a party, you have to slaughter a pig," said An Chan-il, a former North Korean military official who heads a think-tank in the South.
"The nuclear test, together with the ICBM and SLBM tests, are a bridge that the North had to cross to get to the party congress," An said, referring to earlier intercontinental and submarine-launched missile tests.
Chun Yung-woo, who was South Korea`s national security adviser when North Korea last tested a nuclear device, in 2013, said the test, and the claim it was a hydrogen bomb, was Kim`s message to both North Korea and the world.
"He has to show for political purposes before the ruling party congress that he is the man who successfully made the breakthrough in boosting the nuclear capability, both domestically and internationally," Chun told Reuters.
Kim`s tenure has been eventful.
He has made global headlines not only for the weapons programmes but also for gaining weight, hanging out with basketball star Dennis Rodman and disappearing from public view for six weeks in 2014, fuelling speculation about his health.
He reappeared with a limp and a walking stick.
Since taking power after his father died of a heart attack in late 2011, Kim, who is married and believed to be in his early 30s, has replaced his defence chief four times.
He had the last one executed with an anti-aircraft gun, according to the South`s spy agency.
There were seven top officials who joined the young Kim alongside the funeral hearse bearing his father`s body in 2011. They were considered the core supporters of his fledgling leadership.
Of those seven, five have been purged. Among them was Jang Song Thaek, Kim`s uncle and once considered the real power behind the throne, who was executed in December 2013.
By comparison, Kim`s father, who ruled for almost two decades, replaced his defence chief three times.
The young Kim also differs from his father, and is more like his grandfather, in that he is not averse to public speaking.
Unlike his father, Kim Jong Un does not seem especially keen to cultivate ties with China, North Korea`s main diplomatic and economic benefactor, antagonising its neighbour further with the latest nuclear test.
His father, by comparison, courted China with visits until just four months before his death. The younger Kim, educated in Switzerland, is not known to have left North Korea since becoming leader.
For North Koreans, the biggest difference between father and son is the younger Kim`s stewardship over the economy.
Officially, North Korea`s economy is in grim shape, with its national wealth at just $28.4 billion in 2014, according to South Korea`s central bank. On a per capita basis, South Korea is 21 times richer.
But the figures belie growing dynamism in the grey market as the regime casts a blind eye to private enterprise, which may eventually force Kim to implement official reforms.
Militarily, the young Kim has taken North Korea`s arms programme forward by successfully launching a long-range rocket in 2012 and surprising the world by putting an object into space, part of work to develop an intercontinental missile which his father failed to do.
For one South Korean official involved in ties with the North, what`s striking about Kim is his mercurial personality.
"The difference between him and his father is that he is completely unpredictable, and the volatility is huge," said the official, who declined to be identified.
"And he seems to become obsessed when he focuses on something."