(PHNOM PENH, Cambodia) — Nuon Chea, the chief ideologue of the communist Khmer Rouge regime that destroyed a generation of Cambodians, died Sunday, the country’s U.N.-assisted genocide tribunal said. He was 93. Nuon Chea was known as Brother No. 2, the right-hand man of Pol Pot, the leader of the regime that ruled Cambodia from 1975 to 1979. The group’s fanatical efforts to realize a utopian society led to the death of some 1.7 million people — more than a quarter of the country’s population at the time — from starvation, disease, overwork and executions. Researchers believe Nuon Chea was...