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Mengistu Haile Mariam is an Ethiopian former military officer and politician who was the head of state of Ethiopia from 1974 to 1991. He was a member of the Derg, a military junta that overthrew Emperor Haile Selassie in 1974. Mengistu was the leader of the Derg from 1977 to 1991, and he ruled Ethiopia as a Marxist-Leninist dictator.