4. Pol Pot, Vietnam
A dictator, Pol Pot and his army ascended to power in 1975. In 1976, he became the prime minister of the newly created communist government and immediately begun to introduce violent reforms. Due to these policies, the currency was abolished; private property and religion were abolished with the aim of developing a Maoist agrarian community.
In fact, during his time in power approximately 2 million Cambodians were killed due to his policy of forced labor. In 1979, Vietnam invaded Cambodia and Pol Pot was expelled from the capital but continued to rule from exile through his Khmer Rouge army. He retired in 1985 and died out of heart attack in 1998.