Dec. 18, 2020, marks the 142nd birthday of Joseph Stalin, the communist dictator who ruled the Soviet Union for almost three decades. For many people, Stalin is synonymous with mass murder and totalitarianism; his misdeeds are so voluminous and epic in scale that they are incomprehensible.

Historians continually debate just how many deaths Stalin was responsible for. Even a prominent former Soviet and Russian official estimates that Stalin’s victims, whether through famine, purge, or deportation, number around 20 million. Figures such as these are almost impossible for anyone to grasp in full.

The accounts of the Stalin era reveal a man as cruel and ruthless as the numbers suggest. During the Great Terror of the 1930s, Stalin routinely signed off on execution lists with hundreds or thousands of names. In one particularly bloodthirsty day during the Terror, he approved 3,167 executions.

Moments such as these were so commonplace in the Stalin era that the tyrant enjoyed a movie screening immediately afterward, his conscience apparently untroubled by the lives he was ruining.

Stalin’s regime targeted those suspected of being insufficiently dedicated to the communist cause, as well as their innocent family and friends. Millions of Armenians, Bulgarians, Chechens, Germans, Greeks, Jews, Muslims, Poles, and Turks were persecuted for being more loyal to their racial or religious affiliations than to the glorious truths of Karl Marx.

Stalin’s own words reveal his sadistic nature. He once remarked, “The greatest delight is to mark one’s enemy, prepare everything, avenge oneself thoroughly, and then go to sleep.”

Not even Stalin’s closest family and friends were safe — they were often the inevitable targets of his wrath. Stalin’s relatives by marriage, such as Alyosha Svanidze and Pavel Alliluyev, found themselves imprisoned because minor incidents aroused the dictator’s suspicions.

Stalin’s longtime aide Alexander Poskrebyshev begged his boss to release his wife from prison (she had annoyed Stalin by asking him to free her brother). Characteristically, Stalin replied, “Don’t worry, we’ll find you another wife.”

Beyond the unnecessary human cost, one of the most troubling aspects of Stalin’s reign was how convinced his followers were that, despite all of this misery, they were creating a new, better world. Spurred on by the vision of a classless society with perfect equality, they were able to justify atrocities as necessary stumbling blocks on the road to utopia.

Stalin’s interpreter Valentin Berezhkov would later recall, “I believed in Stalin. … We felt we were creating the model for a better society that would be emulated by the rest of the world.” Even Soviet military official Dmitry Volkogonov, whose parents were purged, remembered: “I believed in Stalin. … Everybody thought that Stalin was the foundation of power and happiness and prosperity of the country.”

Historians continue to debate whether or not Stalin was a truly committed communist or simply using Marxist ideology to perpetuate his own power over the Soviet people. Stalin himself used communist terminology throughout his entire career to explain how the world worked. In 1946, he gave a major speech attacking capitalist nations for causing the two world wars. In his last public appearance, in 1952, Stalin continued on this theme, labeling the capitalist bourgeoisie the “arch-enemy” of freedom.

Stalin grew up in a broken home in Georgia mired in the depths of poverty. As a youth living in an authoritarian czarist empire, Stalin saw much in the way of injustice. While in seminary, he turned to communist revolution as the best solution to right the wrongs of his world. Whether or not he continued believing this for the rest of his life is anyone’s guess, but it’s clear that many of his followers were sincere Marxists. Unfortunately for their victims, the communist faithful stopped at nothing to attain the promised utopia.

As scholar Erik van Ree once observed, “The greatest crimes in history have been committed by the sincere — those who believe in their hearts that they are justified in committing their acts.” In doing so, these committed Marxists enabled one of the worst killers in human history.

On the 142nd anniversary of Stalin’s birth, let us remember the key lesson from his life: that those who promise to bring about heaven on earth through revolution and government control, no matter how sincere, often bring about a hell far worse than the one they are trying to escape.

Richard Lim is the co-founder and host of the This American President podcast