We have an exclusive interview with Robert Duvall coming up in the next issue (April). In it, he talks quite a bit about the legendary series "Lonesome Dove" and how it is "The Godfather" of Westerns. One of the things he reveals is that the producers wanted him to wear a Mexican sugarloaf sombrero for the part of Augustus "Gus" McCrae and he absolutely refused to wear it. The hat he ended up wearing (which he himself brought to the set) is actually a 1920s style hat, but today it is iconic and is known far and wide as "The Gus."
The irony is, Duvall also insisted on wearing his own hat in a previous Western "Joe Kidd," and that hat is a modern 1970s rodeo style hat with a pheasant-leaping-off-the-front hatband. Both hats are historically wrong, but it's hard to imagine Gus in anything other than the hat he wore in "Lonesome Dove." Tommy Lee's hat is closer to the style on the Mexican border in that era (1860s), but even Captain Call's head gear is a couple jumps away from the real deal:
But it's the Duvall hat that is embedded in our collective memory as THE style of headgear for an early Texas Ranger. This is one of those cases where artifice triumphs over history, and it's this kind of gerrymandering that drives The Hat Nazi Club members crazy.