Heart attack ended the life of great North Korean president Kim Jong Il.

Kim JOng Il, the rulling president of North Korea, had died on December 17 at 08:30 of a heart attack whilst travelling by train to an area outside Pyongyang-reported North Korean state Television. North Koreans marched by the thousands Monday to their capital's landmarks to mourn Kim Jong Il, many crying uncontrollably and flailing their arms in grief over news of their "dear leader's" death.

North Korean state media proclaimed his twenty-something 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 known to be pursuing nuclear weapons.

South Korea's military went on high alert in the face of the North's 1.2 million-strong armed forces following news of Kim's death, after 17 years in power, on Saturday while carrying out official duties on a train trip. President Barack Obama agreed by phone with South Korean President Lee Myung-bak to closely monitor developments. On the streets of the North Korean capital, Pyongyang, people wailed in grief, some kneeling on the ground or bowing repeatedly. Children and adults laid flowers at key memorials.

Other North Koreans walked in line past a giant painting of Kim Jong Il and his late father, national founder Kim Il Sung, standing together on Mount Paektu, Kim Jong Il's official birthplace. Wreaths were neatly placed below the painting.

Kim Jong Il was the supreme leader of the Democratic People's Republic of Korea (North Korea). He was the General Secretary of the Workers' Party of Korea, the ruling party since 1948, Chairman of the National Defence Commission of North Korea, and the Supreme Commander of the Korean People's Army, the fourth-largest standing army in the world.

A tearful Kim Yong Ho said Kim Jong Il had made people's lives happier. The funeral of dead president is scheduled for 28 December in Pyongyang, with a mourning period lasting until the following day.