Kim Jong-pil, founder of South Korea's once-infamous spy agency and former prime minister, died Saturday in Seoul, his aide said.
He was 92 years old, and is believed to have died of natural causes.
Kim was once a top figure in South Korean conservative politics, and along with former presidents Kim Young-sam and Kim Dae-jung, is considered one of the country's most influential politicians in the 1980s and 1990s.
That era came to be known as the age of the "three Kims".
The trio was banned from politics from 1980 to 1987 when then-military dictator Chun Doo-hwan was in power.
Chun yielded to a popular pro-democracy uprising in 1987 and reinstated the three Kims.
Kim Jong-pil's political career took off in 1961 when he joined then-Major General Park Chung-hee in staging a successful military coup.
He helped Park consolidate his grip on power by establishing the notorious Korean Central Intelligence Agency, which acted as a tool of repression for Park's authoritarian rule.
The Korean CIA wielded unlimited and unchecked power, arbitrarily arresting, torturing and persecuting Park's political opponents.
Kim Jong-pil also led secret negotiations to normalise ties with Korea's former colonial ruler Japan, sparking waves of angry protests across the South in the mid-1960s.
He served as prime minister under Park from 1971 to 75, and again from 1998 to 2000 under then-president Kim Dae-jung.