But a string of surprising diplomatic openings -- including Thursday's stunning offer to meet US President Donald Trump -- has only deepened the enigma surrounding the North Korean leader.

At a lengthy dinner he hosted for South Korean officials on Monday, the man once dismissed by the West as irrational and paranoid presented himself as gracious and confident.

With Trump now planning to meet Kim possibly in May, US officials are working overtime to get a better understanding of what makes him tick.

The prince-like Kim, 34, and his isolated country, remain one of the most impenetrable targets for US intelligence. The most prominent American to have met him is former NBA star Dennis Rodman, who has visited the basketball-mad Kim several times.

- Kim getting good advice? -

Kim's determined push to gain a long range nuclear ballistic missile capability to threaten not only Japan but the United States, and his threats to use it, made US intelligence officials concerned last year that he had a precarious understanding of the world outside Pyongyang.

Kim didn't know the kind of danger he was putting his country in, they said. In December, CIA Director Mike Pompeo openly questioned whether Kim is getting "sound advice" from those around him.

Scott Snyder, a Korea specialist at the Council on Foreign Relations, said that the past few weeks, in which North Korea joined the Winter Olympics in South Korea, invited Seoul officials to Pyongyang, and then offered to freeze nuclear and missile tests for talks with Trump, was possible evidence that Kim may have wised up.

"He's definitely getting some good advice from somewhere now," he told AFP.

He noted that Kim's offer came before he had fully demonstrated he could bomb the United States. That could have been a red line for Washington.

"He stopped short of a full capability, a good move," said Snyder.

Former CIA official and Korea negotiator Joseph DeTrani said two changes have become clear with Kim.

First is the country's success in its military advances. "He's got to feel good about his nuclear missile program," DeTrani said.

But at the same time, he said, Kim now knows how much the international sanctions imposed because of those advances are hurting his country and people.

"I think we know that sanctions are biting and military exercises are intimidating," he said.

One thing Kim is not, DeTrani added, is irrational.

"He seems to be an extremely rational actor, a bit unpredictable, also very ruthless."

- Kim now 'confident', 'graceful' -

Michael Madden, whose group North Korea Leadership Watch does deep dives into all things Kim, said the North Korean leader appears to be moving into a new phase.

Since inheriting his father Kim Jong Il's mantle in 2011, he spent his first six years consolidating power, reportedly liquidating dozens of opponents, trimming some of the military's independent power, and building his internal surveillance capabilities.

Today, Madden said, Kim's regime "is more flexible than we think they are."

That was on display at the dinner with the South Koreans Monday where he showed himself to be "a fairly graceful person," with his rarely-seen wife at his side, readily joking and making fun of himself, Madden said.

The North Koreans released photographs and video from the lavish banquet almost immediately. "It confirms he's confident in having consolidated his power," said Snyder.

Former US diplomat Bill Richardson, who met Kim Jong Il several times, said Kim is on the cusp of achieving what his father and grandfather always wanted: to be treated as equals by Washington.

At just 34, Kim "is unpredictable, sometimes irrational. But he's been underestimated," Richardson said.

"I've long thought he had an agenda, an end-game, and it's obvious that he does. He's evolved from a bomb-throwing leader to a man with a strategic vision," Richardson said.