The Woodrow Call & Augustus McCrae characters were loosely based on the real life Charles Goodnight & Oliver Loving.
Deets was based on the real life Bose Ikard , a slave turned cowboy.
When Ikard died, Goodnight wrote the epitaph quoted in "Lonesome Dove."
It says: "Served with me four years on the Goodnight-Loving Trail, never shirked a duty or disobeyed an order, rode with me in many stampedes, participated in three engagements with Comanches. Splendid behavior."
http://articles.latimes.com/1999/jun/27/local/me-50709Mike