Historian Tony Horwitz tries to separate the truth from the myths that have been built up about the Jamestown “princess” Pocahontas is the most myth-encrusted figure in early America, a romantic “princess” who saves John Smith and the struggling Jamestown colony. But this fairy tale, familiar to millions today from storybook and film, bears little resemblance to the extraordinary young woman who crossed cultures and oceans in her brief and ultimately tragic life. The startling artwork (above), the oldest in the National Portrait Gallery collection, is the only image of Pocahontas taken from life. Made during her visit to London...