North Korean state media proclaimed his youngest son, Kim Jong Un, a "Great Successor," while a vigilant world watched for any signs of a turbulent transition to the untested leader in an unpredictable nation.
The 69-year-old dictator died Saturday of a heart ailment while on a train, state media reported. It took more than two days for news of the death to become public. People were seen weeping in North Korea's capital, Pyongyang, as the announcement of his death came in an emotional statement on national television.
South Korea placed its military on high alert Monday morning after North Korea carried out a short-range missile test.
After a meeting with the Japanese foreign minister, Secretary of State Hillary Clinton said the U.S. and Japan share a common interest in a stable transition in North Korea.
"We reiterate our hope for improved relations with the people of North Korea and remain deeply concerned about their well being," Clinton said at a news conference.
For 17 years, Kim Jong Il ruled North Korea with an iron fist. His father, Kim Il Sung, founded the communist nation after World War II. Once he died in 1994, Kim Jong Il took the reins of power, following in his father's footsteps of total control over nearly all aspects of North Korean life.
"He will be remembered as a person who was responsible for awful things, for the existence of one of the worst dictatorships in probably not only Korean history, but in the world history at least in the 20th and 21st century," said Andre Larkov, a North Korean analyst.
Kim Jong Il's pursuit of nuclear weapons and his military's repeated threats to South Korea and the U.S. bolstered fears of a war or that North Korea might provide weapons of mass destruction to terrorists.
President Barack Obama agreed by phone with South Korean President Lee Myung-bak to closely monitor developments.
"We remain committed to stability on the Korean peninsula, and to the freedom and security of our allies," the White House said in a statement.
Kim Jong Il's funeral is expected to be held next Wednesday. The nation has declared a period of national mourning to last until the day after he's buried.
Some people in Los Angeles' Koreatown said they're hoping for a more diplomatic future for the country.
"I was waiting for him to do something, but he passed away, so I'm happy," said Vivian Lee of Los Angeles. "I think in Korea, maybe we're going to have new things, maybe together now."
Uncertainty about how the longtime dictator's death will affect relations with other countries is not far from people's minds.
"We don't know what anything, what's going to happen," said Stephen Lee of Los Angeles. "We can't expect anything, that's the worst, biggest worry."
Most concerning to some was Kim Jong Un, the third son of Kim Jong Il. Kim Jong Un was educated in Switzerland and is in his late 20s. Many fear his age and inexperience will lead to instability in the region.
The Associated Press contributed to this report.