Reign: 247-210 B.C.

Qin, also called Qin Shihuangdi, united China in 221 B.C. and ruled as the first emperor of the Qin dynasty. He was known to order the killing of scholars whose ideas he disagreed with and the burning of "critical" books.

During his reign, he ordered the construction of a great wall (roughly speaking, the prequel to the modern Great Wall of China), and an enormous mausoleum featuring more than 6,000 life-size terra-cotta soldier figures. Large numbers of conscripts working on the wall died, and those working on the mausoleum were killed to preserve the secrecy of the tomb.

"Every time he captured people from another country, he castrated them in order to mark them and made them into slaves," Hong Kong University's Xun Zhou told the BBC.

Source: British Museum, Britannica, History, BBC

Reign: A.D. 37-41

Caligula was quite popular at first because he freed citizens who were unjustly imprisoned and got rid of a stiff sales tax. But then he became ill, and he was never quite the same again.

He eliminated political rivals (forcing their parents to watch the execution), and declared himself a living god. According to Roman historian Suetonius, Caligula had sex with his sisters and sold their services to other men, raped and killed people, and made his horse a priest.

He was eventually attacked by a group of guardsman and stabbed 30 times.

Source: Biography.com, BBC, "Atlas of History's Greatest Heroes and Villains" by Howard Watson.

Reign: A.D. 434-453

After killing his brother, Attila became the leader of the Hunnic Empire, centered in present-day Hungary, and ended up becoming one of the most feared assailants of the Roman Empire.

He expanded the Hunnic Empire to present-day Germany, Russia, Ukraine, and the Balkans. He also invaded Gaul with the intention of conquering it, though he was defeated at the Battle of Catalaunian Plains.

"There, where I have passed, the grass will never grow gain," he reportedly remarked on his reign.

Source: Britannica, Biography

Reign: A.D. 690-705

Wu went from 14-year-old junior concubine to empress of China. She ruthlessly eliminated opponents by dismissing, exiling, or executing them — even if they were her own family.

The Chinese empire greatly expanded under her rule, and though she had brutal tactics, her decisive nature and talent for government has been praised by historians. Notably, military leaders who were handpicked by Wu took control of large parts of the Korean peninsula.

Source: Britannica

Reign: 1206-1227

Khan's father was poisoned to death when Khan was 9, and he spent time as a slave during his teenage years before he united the Mongol tribes and went on to conquer a huge chunk of Central Asia and China.

His style is characterized as brutal, and historians have pointed out that he slaughtered civilians en masse. One of the most notable examples was when he massacred the aristocrats of the Khwarezm Empire, decimating the ruling class, with unskilled workers taken to be used as human shields.

Source: "Genghis Khan and the Mongol War Machine" by Chris Peers, History.com

Reign: 1483-1498 (as Grand Inquisitor)

Torquemada was appointed Grand Inquisitor during the Spanish Inquisition. He established tribunals in several cities, put together 28 articles to guide other inquisitors, and authorized torture to extract confessions.

He reportedly encouraged King Ferdinand and Queen Isabella to give Spanish Jews the choice between exile or baptism, causing many Jews to leave the country. Historians estimate that Torquemada was responsible for about 2,000 people burning at the stake.

Interestingly, some sources say Torquemada himself came from a family of Jewish converts.

Source: Britannica, "A Psychoanalytic History of the Jews" by Avner Falk

Reign: 1370-1405

Timur led military campaigns through a large chunk of western Asia, including modern Iran, Iraq, Turkey, and Syria, and he founded the Timurid Empire.

In present-day Afghanistan, Timur ordered the construction of a tower made out of live men, each stacked on top of another, and cemented together with bricks and mortar.

He also once ordered a massacre to punish a rebellion, and he had 70,000 heads built up into minarets.

Source: Encyclopedia

Reign: 1448; 1456-1462; 1476

When Vlad III finally became the ruler of the principality of Wallachia, the region was in disarray because of the many feuding boyars. According to the stories, Vlad invited his rivals all to a banquet, where he stabbed and impaled them all. (Impaling was his favorite method of torture.)

Though it's difficult to determine whether this story was embellished, it characterizes Vlad's rule: He tried to bring stability and order to Wallachia through extremely ruthless methods.

Source: Huffington Post, LiveScience, Britannica

Reign: Grand Prince of Moscow: 1533-1547; Czar of All the Russias: 1547-1584

Ivan IV began his rule by reorganizing the central government and limiting the power of the hereditary aristocrats (the princes and the boyars).

After the death of his first wife, Ivan began his "reign of terror" by eliminating top boyar families. He also beat his pregnant daughter-in-law and killed his son in a fit of rage. He earned the nickname "Ivan Grozny" (aka "Ivan the Formidable" — which has been mistranslated to "Terrible").

Source: Biography, Britannica

Reign: 1553-1558

The only child of the notorious King Henry VIII and Catherine of Aragon, Mary I became queen of England in 1553 and soon reinstalled Catholicism (after previous rulers championed Protestantism) as the main religion and married Philip II of Spain — a Catholic.

Over the next few years, hundreds of Protestants were burned at the stake, and for that she earned the nickname "Bloody Mary."

Source: Biography, BBC

Killing spree: 1590-1610

The countess lured young peasant women into her castle, promising them jobs as maids before brutally torturing them to death. According to one account, she tortured and killed as many as 600 girls, though the actual number is likely to be much lower.

Her torture methods included sticking needles under finger nails, covering girls in honey before unleashing bees on them, biting off chunks of flesh, and, most infamously, bathing in the blood of virgins to stay young and beautiful.

Source: Britannica, History

Reign: c. 1789-1794

One of the many influential figures involved in the French Revolution, Robespierre become one of the dominant players during the "Reign of Terror," a period of extreme violence when "enemies of the revolution" were guillotined, arguing that this terror was an "emanation of virtue."

According to historical sources, Robespierre was soon corrupted by power and was executed by guillotine as well.

Source: Biography, BBC

Reign: 1865-1909

King Leopold II "founded" the Congo Free State as "his own" private colony, and went on to make a huge fortune from it by forcing the Congolese into slave labor for ivory and rubber.

Millions ended up suffering from starvation, the birth rate dropped as men and women were separated, and tens of thousands were shot in failed rebellions. Demographers estimate that from 1880 to 1920 the population fell by 50%.

This forced-labor system was later copied by the French, German, and Portuguese officials.

Source: Britannica

Reign: 1913-1918

Historians believe that Talat Pasa was the leading figure in the Armenian genocide. As minister of the interior, he was reportedly responsible for the deportation and ultimately the deaths of some 600,000 Armenians.

He was assassinated in Berlin in 1921 by an Armenian. As an unusual bit of history, Adolf Hitler sent his body back to Istanbul in 1943, hoping to persuade Turkey to join the Axis powers in World War II.

Source: Britannica, The Independent

Reign: 1917-1924

In 1917, Lenin led the October Revolution to overturn the provisional government that had overthrown the czar. About three years of civil war followed, after which the Bolsheviks came out on top and took over the country.

"During this period of revolution, war and famine, Lenin demonstrated a chilling disregard for the sufferings of his fellow countrymen and mercilessly crushed any opposition," the BBC reported.

Source: BBC, Biography

Reign: 1922-1943

After escaping military service, Mussolini founded Italy's Fascist Party, which was supported among disillusioned war veterans, and organized them into violent units called Blackshirts. He began to disintegrate democratic government institutions, and by 1925 he became "Il Duce," or "the leader" of Italy.

Surviving multiple assassination attempts, Mussolini once said: "If I advance, follow me. If I retreat, kill me. If I die, avenge me."

In 1936, Mussolini formed an alliance with Nazi leader Adolf Hitler in which he introduced anti-Semitic policies in Italy. In April 1945, already removed from power, Mussolini tried to flee as Allied forces closed in on him, but he was shot and killed by anti-Fascists and hung upside down in a Milanese square.

Source: Atlas of History's Greatest Heroes and Villains" by Howard Watson.

Reign: 1922-1953

Stalin forced quick industrialization and collectivization in the 1930s that coincided with mass starvation (including the Holodomor in Ukraine), the imprisonment of millions of people in the Gulag labor camps, and the "Great Purge" of the intelligentsia, the government, and the armed forces.

During World War II, Stalin's son Yakov was captured by or surrendered to the German army. The Germans proposed trading Yakov for Field Marshal Paulus, who was captured after the Battle of Stalingrad, but Stalin refused, saying he would never trade a field marshal for a regular soldier.

Source: RT, History, "Joseph Stalin: A Biographical Companion" by Helen Rappaport

Reign: 1933-1945

By the end of 1941, Hitler's German Third Reich empire (and Axis) included almost every country in Europe plus a large part of North Africa.

He also devised a plan to create his ideal "master race" by eliminating Jews, Slavs, gypsies, homosexuals, and political opponents by forcefully sending them to concentration camps, where they were tortured and worked to death.

According to some reports, the Nazis deliberately killed about 11 million people under Hitler's regime. After learning that Soviet forces were closing in on Berlin, Hitler and his wife killed themselves in his Führerbunker.

Source: Atlas of History's Greatest Heroes and Villains" by Howard Watson, New York Review of Books by Timothy Snyder

Reign: 1939-1952

After several meetings with Stalin, Choibalsan adopted the Soviet leader's policies and methods and applied them to Mongolia. He created a dictatorial system and suppressed the opposition, and tens of thousands of people were killed.

Later in the 1930s, he "began to arrest and kill leading workers in the party, government, and various social organizations in addition to army officers, intellectuals, and other faithful workers," according to an report published in 1968.

Source: "Historical Dictionary of Mongolia" by Alan J.K. Sanders

Reign: 1938-1975

With the help of Nazi Germany and Fascist Italy, Gen. Franco overthrew Spain's democratically elected Second Republic during the 1930s.

Under his regime, many Republican figures fled the country, and those who stayed were tried by military tribunals. Catholicism was the official (read: only tolerated) religion, Catalan and Basque languages were prohibited outside the home, and the regime had a vast secret police network.

As Franco got older, however, police controls and censorship began to relax, free-market reforms were introduced, and Morocco gained independence.

Source: Britannica, History.com

Reign: 1949-1976

A communist leader, Mao founded the People's Republic of China. Under his leadership, industry was put under state control, and farmers were organized into collectives. Any opposition was swiftly suppressed.

Mao's supporters point out that he modernized and united China, and turned it into a world superpower. However, others point out that his policies led to the deaths of as many as 40 million people through starvation, forced labor, and executions.

Interestingly, he is sometimes compared to Qin Shi Huang (the first man on this list).

Source: "Atlas of History's Greatest Heroes and Villains" by Howard Watson, Britannica, Biography, BBC, Encyclopedia

Reign: 1975-1979

Pol Pot and his communist Khmer Rouge movement in Cambodia orchestrated a brutal social engineering that aimed to create an agrarian utopia by relocating people into the countryside. Others were put in "special centers" where they were tortured and killed.

Doctors, teachers, and other professionals were forced to work in the fields to "reeducate" themselves. "Anyone thought to be an intellectual of any sort was killed," the BBC reports. "Often people were condemned for wearing glasses or knowing a foreign language."

Up to 2 million Cambodians were executed or overworked or starved to death in just four years.

Source: History, BBC

Reign: 1971-1979

Gen. Amin overthrew an elected government in Uganda via a military coup and declared himself president. He then ruthlessly ruled for eight years, during which an estimated 300,000 civilians were massacred.

He also kicked out Uganda's Asian population (mostly Indian and Pakistani citizens), and spent large amounts on the military, both of which led to the country's economic decline.

Source: History

Reign: 1973-1990

Pinochet overthrew Chile's Allende government in 1973 with the help of a US-backed coup. Reports say numerous people "disappeared" under the regime and as many as 35,000 were tortured. Pinochet died before he could stand trial on accusations of human-rights abuses.

He brought back free-market economic policies, which led to lower inflation and even an economic boom in the late '70s. Notably, Chile was one of the best-performing economies in Latin America from the mid-'80s to the late '90s.

Source: Britannica, Guardian, IMF

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