Given your status as an American Western icon, you may be interested to learn about the literary concepts and attributes that contributed to the development of the genre to which you are most closely associated. To that end, I present James Fenimore Cooper's novel The Deerslayer as one of the first examples of contemporary Western stories of the kind you made films about. Cooper's novel features a masculine, principled protagonists, an obsession with the beauty of the Old West, and plots that emphasize the danger of these surroundings.
The main character of Natty Bumppo, the "Deerslayer," is not unlike the Man With No Name archetype you popularized in so many Italian spaghetti westerns, including A Fistful of Dollars and The Good, the Bad and the Ugly. Bumppo travels mostly alone, and stands apart from the trappers and hunters that he meets along the way; he is also closely connected to the vast emptiness of the American frontier. Deerslayer's only companion is Hurry Harry, an older man much more accustomed to the harsh attributes of the west - this is also quite like your characters in your films. The book is a coming of age tale wherein Deerslayer has to learn that, in order to survive in the Old West, he has to learn to kill: "It is seldom men think of death in the pride of their health and strength" (Chapter 29). At the same time, he remains virtuous: "Truth was the Deerslayer's polar-star" (Chapter 32). He acted as a force for good in his world, much like you also did in your films.
The book itself is a wonderful example of art that demonstrates the beauty of the American west, must as many of your films are. The flowing landscapes of the American Southwest, including their "vast expanse of woods, relieved by a comparatively narrow fringe of cultivation along the sea" as well as other lovely descriptors of the wilderness that awaits the lone traveler (Coooper, Chapter 1). The book's obsession with landscape and the beauty of nature is echoed in the long shots of landscapes and rolling hills and grasses of the plains seen in many Eastwood films. Much like in your films, nature seems to be endless and unalterable by man: " Whatever may be the changes produced by man, the eternal round of the seasons is unbroken" (Chapter 1).
In conclusion, these attributes make The Deerslayer a novel that establishes many of the trappings of the genre: brave, solemn heroes, a coming of age story, the description of the beautiful landscapes of the Old West and more. Hurry Harry and Deerslayer learn a lot about the dangerous nature of the frontier, and the maintenance of goodness and bravery in the face of a cynical and dark world is something that is quintessential to the Western, something you may be well familiar with. If you have not read this book already, Mr. Eastwood, I wholeheartedly recommend it; I think you would find a lot of similarities between the characters in your films and the characters in this book - they all create a romantic picture of the West that is captivating and intriguing, as well as exciting to experience.