Son Sen (Khmer: αα»α ααα pronounced [son seΛn]; 12 June 1930 β 10 June 1997), alias Comrade Khieu (αααα·αααααα) or "Brother Number 89", was a Cambodian Communist politician and soldier. A member of the Central Committee of the Communist Party of Kampuchea/Party of Democratic Kampuchea, the Khmer Rouge, from 1974 to 1992, Sen oversaw the Party's security apparatus, including the Santebal secret police and the notorious security prison S-21 at Tuol Sleng.
Son Sen was responsible for ordering the massacre of more than 100,000 people in the Eastern Zone of Cambodia during the last six months of 1978.