Traditionally, Christopher Columbus has been seen as a hero because of his role as an explorer, facing harsh conditions and the unknown as he made his famous voyage. He wanted to forge a western path to the East Indies so that trade with those nations could be accomplished much more quickly. It took him some time before his lobbying paid off with the Spanish king and queen.
One myth claims Columbus was heroic because he stood his ground against the idea that the earth was flat and that his voyage across the sea was meant to be a way of illustrating the earth's roundness, but this has since been debunked.
As of recent years, many have disputed the heroic image of Columbus due to his harsh treatment of the native Cuban and Hispaniolan peoples, subjecting them to enslavement, torture, and rape at the hands of his men. He was primarily interested in getting land and gold for the Spanish Empire, so his goals were not entirely noble.
He also sought to convert the natives to Catholicism, an act which may have been heroic by the standards of his culture but would be seen in a more negative light now, since this conversion involved the destruction of native cultures and killing those who refused to convert.