Pol Pot, the future Cambodian dictator, was born on this day in 1925 as Saloth Sar to a relatively well-off family. He went to a good school in Paris on a scholarship, where he became interested in communism. He returned home to work as a teacher in 1957, the same year Cambodia gained independence. Now using the nom de guerre Pol Pot, he joined the leadership of the Khmer Rouge, a nascent guerrilla force fighting the government.
When the royal family was overthrown in a military coup, the Khmer Rouge seized the opportunity and kicked off a civil war. In 1975, his group captured the capital Phnom Penh and took control of the country.
Under his rule, residents of every Cambodian city were forced to leave their homes and work in agricultural communes. Those who the Khmer Rouge considered intellectuals, or as having benefited from the old system, were rounded up and killed. Others died from overwork. There was no money, religion, or private property. He would be one of the most violent rulers in world history; by the collapse of his four-year regime, Pol Pot would be responsible for somewhere between 1.5 million and 3 million deaths.
Out of fear that they'd be dominated by Vietnam, the regime also purged people of Vietnamese descent and started to attack its neighboring country. Forced to respond, Vietnam invaded and deposed Pol Pot in just two weeks, going on to occupy Cambodia for 10 years. Pol Pot fled to a border region where he resumed fighting the Vietnamese-sponsored government. Eventually, due to infighting in the Khmer Rouge, he was arrested and sentenced to house arrest for the rest of his life in 1997. He died the following year.
You can read more about Pol Pot's regime at the Association for Asian Studies.