Although he was for nearly two decades America's most powerful and influential literary critic, having become in the early 1920s the first (and, for that matter, last) literary dictator, H. L. Mencken is not generally remembered for his criticism of belles letteres. Still, the fact is that Mencken, more than any other writer, helped to create a sophisticated reading public and thereby pave the way for the literature that came into being in the years just before, during, and after World War I. He performed that service, in large part, as the book critic for the Smart Set magazine between November 1908 and December 1923 and as coeditor (with George Jean Nathan) of that journal for the last nine of those years. With the founding in January 1924 of the American Mercury, Mencken's influence as writer and editor increased dramatically--to the point where the New York Times referred to him in...