As the literary critic Leslie Fiedler argues in his study Love and Death in the American Novel, the classic American literary hero is a soldier, sailor, or cowboy who is brave, laconic, and (ultimately) alone. From Hawkeye in James Fenimore Cooper's Last of the Mohicans through Moby-Dick's Ishmael and Twain's Huckleberry Finn, these characters "light out for the territories" because they don't quite fit in polite society, and they quickly learn self-sufficiency in the wilderness, at sea, or in combat. Hemingway, who identified Huckleberry Finn as the source of all American literature, recognized this archetype, then updated and refined it. The overriding theme of his stories and books was "grace under pressure" — specifically, the ability of "men without women" (the title of an early story collection) to remain calm and competent in the face of life-threatening violence.
Thus, Hemingway heroes like Jake Barnes stoically accept not only war wounds, but the pain of losing whom they love, as well. (Think of Jake's tranquil, orderly San Sebastian vacation after he has, in effect, handed Brett over to Romero.) Whether trout fishing, attending a bullfight, or ordering wine, they are almost scarily adept at what they do, and when the universe conspires to defeat them, they never complain.
The influence of the Hemingway hero can, therefore, be seen in many of the literary soldiers who followed in Jake's footsteps and those of Hemingway's later protagonists, Frederick Henry and Robert Jordan: for instance, the protagonist of James Salter's The Hunters, an account of the exploits of a Korean War jet-pilot squadron. It is even more evident in the archetypal tough-talking detectives of Raymond Chandler (The Big Sleep) and James Ellroy (L.A. Confidential). (Note: Like Jake Barnes and Frederic Henry, Chandler's protagonist Philip Marlowe is a veteran of World War I, as evinced by his trademark trench coat — the coat worn by Allied officers in the trenches of France and Italy. Nearly every character Humphrey Bogart ever played on-screen was influenced by the Hemingway hero.) The cowboys in Cormac McCarthy's Border Trilogy are essentially Hemingway characters, too.