SEOUL, South Korea (AP) — Kim Jong Il, North Korea's mercurial and enigmatic leader whose iron rule and nuclear ambitions dominated world security fears for more than a decade, has died. He was 69.Kim's death 17 years after he inherited power from his father was announced Monday by the state television from the North Korean capital, Pyongyang. The country's "Dear Leader" — reputed to have had a taste for cigars, cognac and gourmet cuisine — was believed to have had diabetes and heart disease. North Korea has been grooming Kim's third son to take over power from his father in the impoverished nation that celebrates the ruling family with an intense cult of personality. South Korea put its military on "high alert" and President Lee Myung-bak convened a national security council meeting after the news of Kim's death. In a "special broadcast" Monday, state media said Kim died of a heart ailment on a train due to a "great mental and physical strain" on Saturday during a "high intensity field inspection." Kim is believed to have suffered a stroke in 2008 but he had 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. Kim Jong Il inherited power after his father, revered North Korean founder Kim Il Sung, died in 1994. He had been groomed for 20 years to lead the communist nation founded by his guerrilla fighter-turned-politician father and built according to the principle of "juche," or self-reliance. 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.