(CNN) -- North Korea's highest-ranking defector has died, South Korea's state-run news media reported Sunday.
Police said Hwang Jang-yop, the highest-ranking North Korean ever to defect to South Korea, was found dead at his home Sunday, the Yonhap news agency reported.
Hwang, 87, appeared to have died of old age, according to police, Yonhap reported.
Police said there were no signs of a break-in at Hwang's home, where a security guard was staying with him, according to Yonhap.
Hwang defected in 1997 after occupying a number of high-level posts in North Korea.
The former chief of North Korea's parliament -- believed to have been a mentor to North Korean leader Kim Jong Il and a confidant of his father, Kim Il Sung -- Hwang is credited with developing the regime ideology of "juche," or "self-reliance."
Hwang had been an outspoken critic of his former homeland since defecting, but said that "ideological warfare," not military action, would help topple the communist regime.
"We don't need to resort to force," he told an audience in Washington earlier this year. "We need to use ideology and markets and diplomacy. We need to take a lesson from the Cold War."
Kim Jong Il made a rare public appearance with his youngest son and heir apparent, Kim Jong Un, at a huge military parade in Pyongyang on Sunday that was billed as the largest ever in North Korea's capital.