By William T. Hagan.
Hagan is one of the pre-eminent authorities and author about the American West. He has authored no less than 8 volumes for the Oklahoma Western Biographies series.
In the author's own words: "Since this study was first published in 1976 it remails the most frequently cites source of information on these people during their reservation period"
That is no wonder when you see the amount of time and resources he pulls together in one cleanly written place. So well researched. So well documented. That is Hagan. I am a big fan of all he does.
Take a look at his Goodnight and Teddy Roosevelt books, as well.