Kim is believed to have suffered in 2008 but appeared relatively vigorous in photos and video from recent trips to China and Russia and in numerous trips around the country carefully documented by state media.
The news came as North Korea prepared for a hereditary succession. Kim Jong Il inherited power after his father, revered North Korean founder Kim Il Sung, died in 1994.
In September 2010, Kim Jong Il unveiled his third son, the twenty-something Kim Jong Un, as his successor, putting him in high-ranking posts.
At this point what caused his death is unknown.
We will update this story as information becomes available.