Oh wow, you mean the genocidal slaver who was too cruel for his own contemporaries was a bad guy????

Explanation: In US school textbooks, Christopher Columbus is either celebrated as a great explorer or mentioned without particular tone in elementary and sometimes middle school textbooks. Modern high school textbooks, however, often reflect a more accurate view of that man - that he was a slaver even before making the journey across the Atlantic, that he never realized that he had found a land other than India (despite nearly everyone else recognizing it by the end of Columbus’s life), and that his early meetings with the natives of the Americas were characterized by open violence and a lust for (mostly nonexistent) riches.

That he was additionally recalled as governor by the Spanish crown for his excessive cruelty (though charges were dropped once he was returned to Spain because of his prior service) and that his entire expedition was based on faulty math (thus making his fortuitous and accidental discovery of the Americas the only thing which saved three crews of sailors from slow death by thirst on the open ocean) were not covered by my high school textbook, but I would not be surprised if they were in others.