The popular image is of him being dark-haired with curly mustaches, while the actual Baron von Richtofen was blonde and clean-shaven. So why does the false image persist?
Because the real Manfred Von Richthofen looks like a golden boy of 25, hardly the stereotypical looks of the dastardly Hun pilot. In any case, the "villain" looks seem to fit more to Rudolph Berthod, see http://en.wikipedia.org/wiki/Rudolph_Berthold
Of course, "dastardly" in the eyes of popular pulp literature and serial films of the 20s and 30s. Veterans would hardly find any connection to the real horror of war through those depictions. It's said that the best WW1 aviation novel is "Winged Victory" (written by a veteran WW1 fighter pilot) and it hardly ever mentions enemy pilots!