Christopher Columbus was awful (but this other guy was not) - The Oatmeal
The oatmeal beats Columbus like a rented mule in this article/presentation. Although sans citation, this isn't sourced, but nonetheless in the aggregate, mostly accurate. What is truly remarkable is that there are countless elementary school classrooms in which students are sitting right now, as you read this, still learning the Columbus myth. Still.
Easy discussion prompt for worthwhile discussion from middle school on up - How does a myth survive?