Life of Plenty Coups circa 1937 (original publication) as seen through the eyes of white culture of that era. Good for comparing versions of what white culture thinks of Indians then and now. I wonder if there is a current bio of Plenty Coups?
There is another by Frank B. Linderman. Judging by another book he wrote about an Indian woman of the same era (Pretty Shield), I'd say the Linderman book would be better.