Denis Julien's first biographer in 1933 called him the "Mysterious D. Julien" because so little was known about him. He was surmised to have been a fur trapper along the Green and Colorado Rivers in the 1830s and not much more than that was known. Modern-day river runners know him from carved inscriptions along those rivers, but little else. This book, however, corrects that, presenting not only the first full-length story of the life of Denis Julien, but also his participation in the fur trade, not only in the American Southwest, but in the Mississippi-Missouri River region as well.