In the course of Irving's tours, Stoker travelled the world, although he never visited Eastern Europe, a setting for his most famous novel. Stoker enjoyed the United States, where Irving was popular. With Irving, he was invited twice to the White House and knew William McKinley and Theodore Roosevelt. Stoker set two of his novels in America and used Americans as characters, the most notable being Quincey Morris. He also met one of his literary idols, Walt Whitman, having written to him in 1872 an extraordinary letter that some have interpreted as the expression of a deeply-suppressed homosexuality.