It's somewhat old hat at this point to point out that Christopher Columbus — in whose name children are off school and mail isn't delivered today — was a homicidal tyrant who initiated the two greatest crimes in the history of the Western Hemisphere, the Atlantic slave trade, and the American Indian genocide.
Rehashing all of his crimes would require a much longer article, not least because evaluating the claims of contemporary primary sources is a somewhat tricky historiographical enterprise. Philadelphia Magazine's Michael Coard has a good survey here; Howard Zinn's work on this is controversial, but you can find a good excerpt at Jacobin and an illustrated version at the Oatmeal.
Here are just a handful of specific cases, mostly culled from Laurence Bergreen's recent biography, Columbus: The Four Voyages, of almost unimaginable cruelty inflicted by Columbus and his crew during their time in the Caribbean.
1) Columbus kidnapped a Carib woman and gave her to a crew member to rape
Bergreen quotes Michele de Cuneo, who participated in Columbus's second expedition to the Americas (page 143):
While I was in the boat, I captured a very beautiful woman, whom the Lord Admiral [Columbus] gave to me. When I had taken her to my cabin she was naked — as was their custom. I was filled with a desire to take my pleasure with her and attempted to satisfy my desire. She was unwilling, and so treated me with her nails that I wished I had never begun. I then took a piece of rope and whipped her soundly, and she let forth such incredible screams that you would not have believed your ears. Eventually we came to such terms, I assure you, that you would have thought she had been brought up in a school for whores.
2) On Hispaniola, a member of Columbus's crew publicly cut off an Indian's ears to shock others into submission
After an attack by more than 2,000 Indians, Columbus had an underling, Alonso de Ojeda, bring him three Indian leaders, whom Columbus then ordered publicly beheaded. Ojeda also ordered his men to grab another Indian, bring him to the middle of his village, and "'cut off his ears' in retribution for the Indians' failing to be helpful to the Spaniards when fording a stream." (Bergreen, 170-171)
3) Columbus kidnapped and enslaved more than a thousand people on Hispaniola
According to Cuneo, Columbus ordered 1,500 men and women seized, letting 400 go and condemning 500 to be sent to Spain, and another 600 to be enslaved by Spanish men remaining on the island. About 200 of the 500 sent to Spain died on the voyage, and were thrown by the Spanish into the Atlantic. (Bergreen, 196-197)
4) Columbus forced Indians to collect gold for him or else die
Columbus ordered every Indian over 14 to give a large quantity of gold to the Spanish, on pain of death. Those in regions without much gold were allowed to give cotton instead. Participants in this system were given a "stamped copper or brass token to wear around their necks in what became a symbol of intolerable shame." (Bergreen, 203)
5) About 50,000 Indians committed mass suicide rather than comply with the Spanish
Bergreen explains, page 204:
The Indians destroyed their stores of bread so that neither they nor the invaders would be able to eat it. They plunged off cliffs, they poisoned themselves with roots, and they starved themselves to death. Oppressed by the impossible requirement to deliver tributes of gold, the Indians were no longer able to tend their fields, or care for their sick, children, and elderly. They had given up and committed mass suicide to avoid being killed or captured by Christians, and to avoid sharing their land with them, their fields, groves, beaches, forests, and women: the future of their people.
6) 56 years after Columbus's first voyage, only 500 out of 300,000 Indians remained on Hispaniola
Population figures from 500 years ago are necessarily imprecise, but Bergreen estimates that there were about 300,000 inhabitants of Hispaniola in 1492. Between 1494 and 1496, 100,000 died, half due to mass suicide. In 1508, the population was down to 60,000. By 1548, it was estimated to be only 500.
Understandably, some natives fled to the mountains to avoid the Spanish troops, only to have dogs set upon them by Columbus's men. (Bergreen, 205)
7) Columbus was also horrible to the Spanish under his rule
While paling in comparison to his crimes against Caribs and Taino Indians, Columbus's rule over Spanish settlers was also brutal. He ordered at least a dozen Spaniards "to be whipped in public, tied by the neck, and bound together by the feet" for trading gold for food to avoid starvation. He ordered a woman's tongue cut out for having "spoken ill of the Admiral and his brothers."
Another woman was "stripped and placed on the back of a donkey … to be whipped" as punishment for falsely claiming to be pregnant. He "ordered Spaniards to be hanged for stealing bread" (Bergreen, 315-316). Bergreen continues:
He even ordered the ears and nose cut off one miscreant, who was also whipped, shackled, and banished from the island. He ordered a cabin boy's hand nailed in public to the spot where he had pulled a trap from a river and caught a fish. Whippings for minor infractions occurred with alarming frequency. Columbus ordered one wrongdoer to receive a hundred lashes — which could be fatal — for stealing sheep, and another for lying about the incident. An unlucky fellow named Juan Moreno received a hundred lashes for failing to gather enough food for Columbus's pantry.
8) Settlers under Columbus sold 9- and 10-year-old girls into sexual slavery
This one he admitted himself in a letter to Doña Juana de la Torre, a friend of the Spanish queen: "There are plenty of dealers who go about looking for girls; those from nine to ten are now in demand, and for all ages a good price must be paid."
9) Indian slaves were beheaded when their Spanish captors couldn't be bothered to untie them
Benjamin Keen, a historian of the Spanish conquest of the Americas, noted that multiple sources confirmed accounts of "exhausted Indian carriers, chained by the neck, whose heads the Spaniards severed from their bodies so they might not have to stop to untie them."
Update: A prior version of this article used another translation of Columbus's letter that wasn't as clear that he was speaking of 9- and 10-year-old girls; a different translation was substituted for clarity.