We see in The Virginian the development of the concept of "nature's nobleman" and its move to a Western setting. This is an outgrowth of other novels popular at the time, some mentioned in John Nesbitt's post above. This new hero is exalted not because of rank, blood, or birth but because of his intrinsic goodness. Also, there is some feeling that association with the earth, nature, animals, and unspoiled wilderness contributes to his nobility.
The cowboy as nature's nobleman is often eloquent and wise. He is fair and administers frontier justice. He is strong, a sharp shooter, beloved by all animals especially horses, and ever respectful and worshipful of women.
Contrast this to Brokeback Mountain, where Annie Proulx takes great pains to show that the protagonists are not nature's noblemen. In fact, the first sentence reads, "They were raised on small, poor ranches in opposite corners of the state...both high-school drop-out country boys with no prospects, brought up to hard work and privation, both rough-mannered, rough-spoken, inured to the stoic life." Jack is far from a sharp-shooter and provokes fits of crow-hopping in his horse, and both of them are indifferent to women, Ennis treating his wife so poorly that she divorces him. In spite of this, we can see echoes of The Virginian in both Jack and Ennis.