The fourth Republic of Korea (Korean: 4; Hanja: ; RR: Je-sa Gonghwaguk) was the government of South Korea from November 1972 to March 1981.

The Fourth republic was founded on the approval of the Yushin Constitution in the 1972 constitutional referendum, codifying the de facto dictatorial powers held by President Park Chung-hee, and succeeding the third republic. Park and his Democratic Republican Party ruled under the centralized and authoritarian Yushin System until the assassination of Park on 26 October 1979. The Fourth Republic entered a period of political instability under Park's successor, Choi Kyu-hah, and the escalating martial law declared after Park's death. Choi was unofficially overthrown by Chun Doo-hwan in the coup d'tat of December Twelfth in December 1979, and began the armed suppression of the Gwangju Democratization Movement against martial law. Chun launched the coup d'tat of May Seventeenth in May 1980, establishing a military dictatorship under the National Council for Reunification and dissolving the National Assembly, and was elected president by the council in the August 1980 presidential election. The Fourth republic was dissolved on the adoption of a new constitution in March 1981 and replaced with the Fifth Republic of Korea.

Park Chung-hee (Korean: 박정희, IPA: [pʰak̚ t͡ɕʌŋ hi]; 14 November 1917 – 26 October 1979) was a South Korean politician and army general who served as the leader of South Korea from 1961 until his assassination in 1979; ruling as a de facto military dictator from 1961 to 1963, then as the country's de jure third president from 1963 to 1979.

Before his presidency, he was a military leader in the South Korean army, and was the second-highest ranking officer in the army. He first came to power after leading a military coup in 1961, which brought an end to the interim government of the Second Republic. After serving for two years as chairman of the military junta, the Supreme Council for National Reconstruction, he was elected president in 1963, ushering in the Third Republic. Seeking to bring South Korea into the developed world, Park began a series of economic policies that brought rapid economic growth and industrialization to the nation that eventually became known as the Miracle on the Han River. South Korea possessed one of the fastest growing national economies during the 1960s and 1970s as a result. According to the Gapminder Foundation, extreme poverty was reduced from 66.9 percent in 1961 to 11.2 percent in 1979, making one of the fastest and largest reductions in poverty in human history. This growth also encompassed declines in child mortality and increases in life expectancy. From 1961 to 1979 child mortality declined by 64%, the third-fastest decrease in child mortality of any country with over 10 million inhabitants during the same period.Under his government, South Korea saw the development of chaebol, family companies supported by the state similar to the Japanese zaibatsu. These companies include Hyundai, LG, and Samsung. However, the economic development of South Korea was pursued at great sacrifice to the working class: the government did not recognise a minimum wage or weekly leave, imposed free work periods for its own benefit, and twelve-hour workdays were the norm. In addition, trade unions and industrial action were prohibited. Despite the above points, which takes a retrospective view from a position of prosperity, the fact that people who were in poverty were able to work stable jobs, was welcomed by the vast majority of South Koreans.Although popular during the 1960s, by the 1970s, Park's popularity started to plateau. This resulted in closer than expected victories during the 1971 South Korean presidential election and the subsequent legislative elections. Following this, in 1972, Park declared martial law and amended the constitution into a highly authoritarian document, called the Yushin Constitution, ushering in the Fourth Republic. During this time, political opposition and dissent was constantly repressed and Park had complete control of the military, and much control over the media.

Park was assassinated on 26 October 1979 by his close friend Kim Jae-gyu, the director of the Korean Central Intelligence Agency, at a safe house in Seoul following the student uprising later known as the Bu-Ma Democratic Protests. Cha Ji-chul, chief of the Presidential Security Service, was also fatally shot by Kim. Kim and his accomplices were tortured, convicted and executed for the assassination. Choi Kyu-hah became Acting President pursuant to Article 48 of the Yushin Constitution. Major General Chun Doo-hwan quickly amassed sweeping powers after his Defense Security Command was charged with investigating the assassination, first taking control of the military and the KCIA before installing another military junta and finally assuming the presidency in 1980. Whether the assassination was spontaneous or premeditated is something that remains unclear today—the motivations of Kim Jae-gyu are still debated.

Economic growth continued after Park's death and after considerable political turmoil in the wake of his assassination and the military Coup d'état of December Twelfth, the country eventually democratized. Later presidents included Kim Dae-jung, a pro-democracy chief opponent of Park who was kidnapped, arrested, and sentenced to death by the Park administration, and Park Geun-hye, Park's eldest daughter who was the first female president of South Korea and was impeached, removed from office, and later sentenced to 27 years in prison as a result of an influence-peddling scandal.Park is a controversial figure in modern South Korean political discourse and among the South Korean populace in general for his dictatorship and undemocratic ways. While some credit him for sustaining the Miracle on the Han River, which reshaped and modernized South Korea, others criticize his authoritarian way of ruling the country (especially after 1971) and for prioritizing economic growth and contrived social order at the expense of civil liberties. According to a 2019 poll by Gallup Korea, 49% of older Koreans (aged 60+) see Park as the greatest president, while only 5% of young Koreans (aged 15-18) see Park as the greatest president, making him the second most popular Korean president while simultaneously one of the most controversial and memorable.