Kim Jong Il (Creative Commons).

Kim died "from great mental and physical strain" on board a train during one of his field trips outside the capital, the official news agency KCNA said.

It is believed that Kim, 69, suffered a stroke in 2008 despite appearing "relatively vigorous" during recent public trips to China and Russia, according to the Associated Press. He was believed to have had diabetes and heart disease.

Kim became head of the North Korean communisty party after the passing of his father, and North Korean founder, Kim Il Sung in 1994, according to Bloomberg.

From Bloomberg:

…Kim was a chain-smoking recluse who ruled for 17 years after coming to power… and resisted opening up to the outside world in order to protect his regime.

The potential succession of his little-known third son, Kim Jong Un, threatens to trigger a dangerous period for the Korean peninsula, where 1.7 million troops from the two Koreas and the U.S. square off every day.

“Kim Jong Il inherited a genius for playing the weak hand and by keeping the major powers nervous, continuing his father’s tradition of turning Korea’s history of subservience on its head,” said Michael Breen, the Seoul-based author of “Kim Jong Il: North Korea’s Dear Leader,” to Bloomberg. “We have entered an uncertain moment with North Korea.”

According to Foreign Policy, Kim Jong Il's third and youngest son, Kim Jong-Un, was nominated to succeed his father in January of 2009.

View the story "More on death of Kim Jong Il" on Storify]

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