Park Tong-jin, a former foreign minister, died of natural causes Monday at the age of 91, his family said.

The longest-serving South Korean foreign minister between 1975 and 1980 under the Park Chung-hee administration, Park Tong-jin also worked as a unification minister, an ambassador to the United States and a two-term lawmaker.

He dealt with Seoul’s relations with Washington during the turbulent period of the late 1970s. Then-President Park Chung-hee was assassinated by his intelligence chief and a group of soldiers led by Maj. Gen. Chun Doo-hwan seized power in a military coup after Park’s death in 1979. (Yonhap News)