Khieu Samphan in the context of "Fall of Phnom Penh"

Khmer Rouge is the name that was popularly given to members of the Communist Party of Kampuchea (CPK), and by extension to Democratic Kampuchea, which ruled Cambodia between 1975 and 1979. The name was coined in the 1960s by Norodom Sihanouk to describe his country's heterogeneous, communist-led dissidents, with whom he allied after the 1970 Cambodian coup d'état.

The Kampuchea Revolutionary Army was slowly built up in the forests of eastern Cambodia during the late 1960s, supported by the People's Army of Vietnam, the Viet Cong, the Pathet Lao, and the Chinese Communist Party (CCP). Although it originally fought against Sihanouk, the Khmer Rouge changed its position and supported Sihanouk following the CCP's advice after he was overthrown in a 1970 coup d'état by Lon Nol who established the pro-American Khmer Republic. Despite a massive American bombing campaign (Operation Freedom Deal) against them, the Khmer Rouge won the Cambodian Civil War when they captured the Cambodian capital and overthrew the Khmer Republic in 1975. Following their victory, the Khmer Rouge—who were led by Pol Pot, Nuon Chea, Ieng Sary, Son Sen, and Khieu Samphan—immediately set about forcibly evacuating the country's major cities. In 1976, they renamed the country Democratic Kampuchea.

Nuon Chea (Khmer: នួន ជា; born Lao Kim Lorn; 7 July 1926 – 4 August 2019), also known as Long Bunruot (Khmer: ឡុង ប៊ុនរត្ន) or Rungloet Laodi (រុងឡឺត ឡាវឌី Thai: รุ่งเลิศ เหล่าดี), was a Cambodian politician and revolutionary who was the chief ideologist of the Khmer Rouge. He also briefly served as acting Prime Minister of Democratic Kampuchea. He was commonly known as "Brother Number Two" (Khmer: បងធំទី២), as he was second-in-command to Khmer Rouge leader Pol Pot, General Secretary of the Party, during the Cambodian genocide of 1975–1979. In 2014, Nuon Chea received a life sentence for crimes against humanity, alongside another top-tier Khmer Rouge leader, Khieu Samphan, and a further trial convicted him of genocide in 2018. These life sentences were merged into a single life sentence by the Trial Chamber on 16 November 2018. He died while serving his sentence in 2019.