Following are five facts about Khmer Rouge "Brother Number Two" Nuon Chea, who was taken into custody by the United Nations-backed "Killing Fields" tribunal on Wednesday.
Of the surviving Khmer Rouge cadres, Nuon Chea is believed to be the one most responsible for the deaths of the regime's estimated 1.7 million victims. Most were executed or died of starvation, torture or disease.
-- Born Long Bunruot around 1923, he grew up in the northwestern province of Battambang. His family is thought to have had Chinese ancestry.
Like many Khmer Rouge leaders, he used a number of aliases throughout his life, including Long Rith, Nuon, Second Brother and Grand Uncle.
-- Unlike many of Pol Pot's inner circle, Nuon Chea did not study in Paris. Instead, he read law at Bangkok's prestigious Thammasat University, where he became a member of the Thai Communist Party.
After cutting a deal with the Cambodian government in December 1998, he lived in a small wooden house in forests along the Thai border. His university connections and fluent Thai gave him ready access to medical treatment in Bangkok.
-- Was appointed Deputy Secretary of the Communist Party of Kampuchea (the Khmer Rouge's name for Cambodia) in 1960, a position that put him in charge of party and state security.
This included Phnom Penh's notorious S-21 interrogation and torture centre at the capital's Tuol Sleng high school.
-- On Jan 5, 1979, two days before the Vietnamese army overran Phnom Penh, Nuon Chea ordered S-21 head Duch, who has been charged with crimes against humanity, to kill all remaining prisoners.
Despite Duch's compliance, seven people are known to have survived. Along with Duch, they are expected to be key witnesses at the trial.
-- At a December 1998 news conference confirming his peace deal with Phnom Penh, Nuon Chea issued an apology of sorts to the Cambodian people. Those who had lived through four years of horror under the regime were unimpressed.
"Naturally, we are sorry -- not only for the lives of the people, but also for the animals. They all died because we wanted to win the war," he said.
(Sources: Reuters, "Pol Pot: The History of a Nightmare" by Philip Short)