His ultimate motives, like many details of his life, are uncertain. Since taking power, Mr. Kim has yet to travel abroad or host a visit from another state leader. Only a few people outside North Korea have been allowed to meet with him — the former basketball star Dennis Rodman, a Japanese sushi chef, the vice presidents of Cuba and China.
What little is known of Mr. Kim’s record suggests ruthlessness — and some ideological flexibility.
South Korean intelligence officials say Mr. Kim has executed scores of senior officials, including his own uncle, a wily power broker who had been seen as his mentor. He is also assumed to have ordered the assassination of his half brother, who was poisoned by VX nerve agent at the Kuala Lumpur International Airport in Malaysia in February.
Yet Mr. Kim is also credited with loosening state controls on the economy and engineering modest growth, and regaining some of the public confidence that the dynastic regime enjoyed under his grandfather and lost under his father, whose rule is remembered for a devastating famine.
“Smart, pragmatic, decisive,” Andrei Lankov, a North Korea expert at Kookmin University in Seoul, said of Mr. Kim. “But also capricious, moody and ready to kill easily.”
One subject on which Mr. Kim has not wavered is the nuclear program. His father held out the possibility of scrapping the program in return for economic aid and security guarantees and even struck a deal with the Clinton administration, though the North later violated it. But Mr. Kim has taken a more aggressive approach.
Three of North Korea’s five nuclear tests have come under his watch, and there are signs that the country is preparing for another one. North Korea has also conducted about 80 missile tests under Mr. Kim, more than twice as many as under his father and grandfather combined.
The nation crossed a major threshold with the last two missile tests, on July 4 and July 28, which analysts said demonstrated intercontinental ballistic missiles capable of hitting Alaska and, in the most recent test, the mainland United States.
North Korean state media showed Mr. Kim present at both tests, wearing a suit with a Mao-style collar, surrounded by soldiers and smiling broadly.
A Mysterious Heir
Mr. Kim first appeared in North Korean state media in September 2010, little more than a year before he succeeded his father as supreme leader. The reports said that he had been appointed a…