October 26 Incident
KCIA director Kim Jae-gyu shot and killed President Park Chung-hee, bringing down the Yushin system.

中央通訊社 · Public domain · Source
On 26 October 1979, at a KCIA safe house in Gungjeong-dong, Seoul, KCIA director Kim Jae-gyu shot and killed President Park Chung-hee and his chief bodyguard. There had been conflict within the regime over how to deal with the Busan–Masan protests.
The Yushin system collapsed. Prime Minister Choi Kyu-hah became acting president and was elected president by the National Conference for Unification in December.