Answer:
He was the leader of the Cambodian communist movement known as the Khmer Rouge and the de facto leader of Cambodia in mid-1975. During his time in power, Pol Pot imposed a version of agrarian collectivization, forcing city dwellers to relocate to the countryside to work in collective farms and forced labor projects, toward a goal of "restarting civilization".
The combined effects of slave labor, malnutrition, poor medical care, and executions resulted in the deaths of an estimated 1.7 to 2.5 million people, approximately 21% of the Cambodian population.
By some views he ranks behind only Hitler and Stalin as the worst mass murderer of the 20th century.