Ieng Sary was the co-founder and senior member of the Khmer Rouge and one of the main architects of the Cambodian Genocide. He was a member of the Central Committee of the Communist Party of Kampuchea led by Pol Pot and served in the 1975–79 government of Democratic Kampuchea as foreign minister and deputy prime minister. He was known as "Brother Number Three", as he was third in command after Pol Pot and Nuon Chea. His wife, Ieng Thirith, served in the Khmer Rouge government as social affairs minister. Ieng Sary was arrested in 2007 and was charged with crimes against humanity but died of heart failure before the case against him could be brought to a verdict.

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