Who is Mr. Winterbourne from Tales of Henry James: The Texts of the Stories, the Author on His Craft, Background and Criticism and what is their importance?

Mr. Winterbourne is the narrator of the story, a twenty-seven-year old man who lives in Geneva. He is represented as both a student and a young man having an affair with an older, married woman. Visiting his aunt in the resort town of Vevey, he meets Daisy Miller. She is a young American woman completely unlike the European women he knows, and he cannot understand her or clearly categorize her. Compared to Daisy Miller, Winterbourne is glum, stodgy, formal, weak and no fun at all.