To what extent was dances with Wolves based on fact? Was there such a person as Lt John Dunbar?

Dances with Wolves was by any standard a film masterpiece; the story was moving, the action riveting the music sublime, the scenery was stunning and the film carried an important message that is as valid today as ever ie we need to control our greed, we need to live in balance with Nature and stop abusing her, we need to learn to respect all forms of life, animals, all people alike, irrespective of whether they are Jews, Moslem's, Christians , Sikhs, Chinese, Germans, Japanese etc. The Indians of North America, like the Incas who fled to Machu Picchu , they showed us some valuable lessons on how to live and how to respect Nature, how to respect animals rather than subduing them and subjecting them to endless pain.