Pol Pot. His leadership caused 1/4 Cambodians to be shot, tortured or starved to death. The Khmer Rouge were probably among the most brutal sadists that I've ever read about. Sure, his death count wasn't as high as Stalin's, Hitler's or Mao's, but it was the system he set up that showed how evil he was.
When the Khmer Rouge took power, everyone, EVERYONE was forced out of their homes into poorly made shanty villages. Patients were ordered out of hospital - if they were too sick, they just shot them. Anyone with glasses was suspected of being an "intellectual", and they too would be shot. Anyone speaking any other language than the Khmer Rouge's official Cambodian language would be shot. If you were not ethnically Cambodian, you'd be shot. Anyone who even LOOKED middle class would be shot. Teachers, doctors, anyone thought to retain a hint of "the old ways" had to be executed, because the Khmer Rouge wanted to take everything back to "Year Zero", as in completely obliterate the past in order to have a clean slate for the future. The Chinese Communists tried a similar thing during the "Cultural Revolution", but they were no where near as harsh and sadistic as the Khmer Rouge (they let people live to be re-educated, whereas the Khmer's just shot anyone they wanted).
Even if you weren't shot, life was not pleasant. You had to wear the clothes that were given to you. If you moved without permission, you'd be shot. If you spoke out of turn, you'd be shot. If you failed to grow enough crops, because the authorities didn't give you the proper farming equipment, guess who got shot? You did. If a family member committed a crime, their child or relative was expected to kill them. There are pictures of six year old kids being instructed on how to behead "class enemies".
And if you were expected of being a spy? You were done for - you had no chance at living. They'd electrocute you, burn you, break your bones until you confessed. The authorities were paranoid and insane - they'd accuse people of being a member of the KGB, the CIA AND the Vietnamese communist party (the Khmer Rouge, despite being communist, HATED the Vietnamese and the Russians, and killed anyone suspected of being allied with them). They forced innocent people to confess to outrageous, outlandish crimes, just so that they could kill them.
The Khmer Rouge committed genocide. All Vietnamese or Chinese in Cambodia who weren't driven out were executed (Surprisingly, the Chinese government who supported the Khmers at the time, had no problem with this. Usually the Chinese do raise a fuss if their citizens are mistreated). The Khmer rouge starved and tortured its own citizens. They transformed Cambodia into a giant insane asylum/prison, only it was the criminal maniacs who ran the place.
A cursory glance at the history of Cambodia and the atrocities committed by the Khmer Rouge reveals them to be just..... insane. That's the only word I can use to describe the Khmers - they were barking mad. They were LITERALLY crazy, crazy with anger and hatred. They were lunatic fanatics seeing "capitalist" demons in every man woman and child, and thought that it was perfectly acceptable to "cleanse" their country by drenching it in blood. They are the scariest people I have ever read about. Scarier than the Nazis even. Sure the Nazis KILLED more people, but they weren't as clearly INSANE as the Khmers.
And Pol Pot was the man who started it all. I honestly think he's more evil than Hitler. He was less destructive. But he was more evil.
