Khmer people (ខ្មែរ, English pronunciation: /ˈkmɛər/ or /kəˈmɛər/) are the predominant ethnic group in Cambodia, accounting for approximately 90% of the 14.8 million people in the country. They speak the Khmer language, which is part of the larger Mon–Khmer language family found throughout Southeast Asia. The majority of the Khmer are followers of the Khmer style of Buddhism, a highly syncretic version which blends elements of Theravada Buddhism, Hinduism, animism and ancestor-spirit worship. Significant populations of Khmers reside in adjacent areas of Thailand (Northern Khmer) and the Mekong Delta region of neighboring Vietnam (Khmer Krom).

Migrations into the mainland regions of Southeast Asia from the north continued well into historic times.^{[citation needed]} Most scholars believe they came at least 3,000 years ago, much earlier than Tai people who now inhabit many parts of what was originally Austroasiatic territory. The reason they migrated into Southeast Asia is generally debated, but scholars believe that Mon–Khmer were pushed down by invading Sino-Tibetans from the north as evident by Austroasiatic vocabulary in Chinese or because of agricultural purposes as evident by their migration routes along major rivers. The Khmer are relatives to the Mon who settled further to the west.

Saloth Sar (19 May 1925 – 15 April 1998), better known as Pol Pot (Khmer: ប៉ុល ពត), was a Cambodian Maoist revolutionary who led the Khmer Rouge from 1963 until his death in 1998. From 1963 to 1981, he served as the General Secretary of the Communist Party of Kampuchea. From 1976 to 1979, he also served as the prime minister of Democratic Kampuchea. Pol Pot became leader of Cambodia on April 17, 1975. During his time in power he imposed agrarian socialism, forcing urban dwellers to relocate to the countryside to work in collective farms and forced labor projects. The combined effects of forced labor, malnutrition, poor medical care, and executions resulted in the deaths of approximately 21% of the Cambodian population. In all, an estimated 1.7 to 2.5 million people (out of a population of slightly over 8 million) died as a result of the policies of his three-year premiership.

In 1979, after the Vietnamese invasion of Cambodia, Pol Pot fled to the jungles of southwest Cambodia, and the Khmer Rouge government collapsed. From 1979 to 1997, he and a remnant of the old Khmer Rouge operated near the border of Cambodia and Thailand, where they clung to power, with nominal United Nations recognition as the rightful government of Cambodia. Pol Pot died in 1998 while under house arrest by the Ta Mok faction of the Khmer Rouge. Since his death, rumours that he was poisoned have persisted.