PYONGYANG, North Korea >> With the sudden death of his father, Kim Jong Un went from being North Korea’s "Respected General" to "Great Successor" — a heady and uncertain promotion for a young man virtually unknown even to the North Korean people just a year ago.

Word of Kim Jong Il’s death, announced Monday two days after he suffered a fatal heart attack, thrusts his 20-something son in the spotlight as the future head of a nation grappling with difficult nuclear negotiations and chronic food shortages.

Within hours of breaking the news of his father’s death, state media urged the nation’s people to rally around Kim Jong Un and to "faithfully revere" their next leader. The son has not appeared publicly since the announcement of his father’s death.

The death speeds up a succession process that began in earnest a little more than a year ago — scant time to gain experience, build political clout and allay skepticism at home and abroad that he can lead a nation of 24 million. His father, by contrast, had 20 years of grooming before his father, North Korea founder Kim Il Sung, passed away in 1994.

News of Kim’s death shocked a nation largely kept in the dark about their leader’s health even after he suffered a stroke in 2008. Abroad, there was widespread speculation throughout 2009 about who would succeed the iron-fisted ruler.

Kim Jong Un’s emergence in September 2010 as the anointed successor settled the question of which of Kim Jong Il’s three known sons was chosen as the third-generation leader in a family dynasty that has ruled since North Korea’s post-World War II inception in 1948.

And his status as his father’s anointed successor has become clear over the course of the past year.

After appointing him vice chairman of the Central Military Commission of the ruling Workers’ Party, Kim Jong Il unveiled the son to the world just weeks later at a massive military parade to celebrate a key party anniversary.

With the world’s media in attendance and transmitting live video, the young son appeared on the balcony of the Grand People’s Study Hall in a blue suit, waving as tanks loaded with long-range missiles barreled by.

Since that first glimpse of the son, North Koreans have seen him regularly on state TV, in the Pyongyang Times newspaper and in the Korean Central News Agency as he accompanied his father on trips around the country.

Stocky and youthful, he bears more than a passing resemblance to his grandfather, Kim Il Sung, as a young man — a similarity that plays into the emphasis on lineage and legacy as just cause to make him leader.

He began appearing with his father at state events and reportedly ran the country when Kim traveled to Russia and China, and is credited at home with orchestrating a deadly November 2010 artillery attack on a front-line South Korean island that nearly brought the foes to the brink of another war.

Kim Jong Il’s leadership was defined by his "songun" policy of putting the powerful military first. Kim Jong Un’s formal ascension will usher in a new era of leadership — but it remains to be seen what direction he will take the nation of 24 million people.

"It is impossible to say with certainty what his era will look like. Trying to anticipate the near future is tough enough," said Andray Abrahamian, executive director of the Choson Exchange, a Singapore-based nonprofit group that facilitates educational exchange with North Korea. "We expect greater caution and less willingness to try new things in the near term, making our programs more difficult to run. Things look like they’re locking down already."

North Koreans have been told Kim Jong Un graduated from Kim Il Sung Military University; speaks several foreign languages, including English; and is a whiz at computing and technology.

But they have not been told much else.

He is said to celebrate his birthday in January, but the year — or even the name of his mother — have not been revealed publicly. Even his name, though whispered for years, was never published in state media until the announcement in September 2010 that he had been promoted to four-star general.

"There is a rumor that he is married, but officially we don’t know," said Yoon Deok-ryong, who specializes in North Korean economic reform at the Korea Institute for International Economic Policy in Seoul.

The visits have also provided hints to what areas Kim Jong Un may favor when he formally takes power. Newly opened shops and factories churning out goods using digital technology have been favorite spots for a man said to like computers.

Two songs in vogue in Pyongyang are considered odes to Kim Jong Un: "Footsteps," an obvious reference to his role in carrying out his family’s legacy, and "Song of CNC," or Computerized Numerical Control, better known elsewhere as digital technology.

In September, he spent hours at one of Pyongyang’s showcase shops, a meat and fish shop on Pothongmun Street that sells whale meat, frozen quail and kielbasa, manager Ri Un Suk told The Associated Press in October.

His visit is proudly displayed on a plaque affixed to the wall, a tradition that until recently was reserved for his father and grandfather.

"He may be the future leader, but he’s still a good son to his father," she said. "I was impressed by his loyalty as well as his wisdom."

A year ago, after he made his public debut, he was familiarly referred to as the "Young General."

In recent months, signs and plaques formally acknowledging him as the next leader began appearing with the title "Respected General."

On Monday, the state-run Korean Central News Agency called him the "Great Successor," and urged the people to rally around their next leader.

Kim Jong Un is expected to lean on members of his father’s inner circle, including his aunt, Kim Jong Il’s sister Kim Kyong Hui; her husband, Jang Song Thaek; and other Kim Jong Il confidants, experts said.

"Even though Kim Jong Un has been appointed as the successor, they may form a committee to rule the country at first," Yoon said. "His power succession is not completed yet."

There are concerns about instability due to his age and inexperience, said Narushige Michishita, an expert at the National Graduate Institute for Policy Studies in Tokyo.

But his age may win him backing among the young policymakers of his generation who have developed a taste for cellphones and computers, he said.

"Those people will be running the country in coming decades," Michishita said. "So in that sense we can expect some new things, but we don’t know if that will result in political transformation."

Kim Jong Un is known to have studied for a few years in Switzerland as a teen and is believed to speak some German and French as well as English, though experts caution against thinking of him as reform-minded just because he lived in the West.

"I wouldn’t draw huge conclusions from the fact that he spent a year or two in Europe as a boy," Delury said. "But you know, he’s significantly younger, and generational shifts happen no matter wherever you are in the world, including North Korea, so he is going to have a different orientation."

Apart from these few tantalizing details, much remains unknown about Jong Un or the real breadth of his power.

"There’s much uncertainty," Yoon said. "Because we don’t know who’s really in charge."

___

Associated Press writers Alexa Olesen in Beijing, Malcolm Foster in Tokyo and Foster Klug in Seoul, South Korea, contributed to this report.