No film critic has ever been as influential--or as beloved-- as Roger Ebert. Over more than four decades, he built a reputation writing reviews for the Chicago Sun-Times and, later, arguing onscreen with rival Chicago Tribune critic Gene Siskel and later Richard Roeper about the movies they loved and loathed. But Ebert went well beyond a mere "thumbs up" or "thumbs down." Readers could always sense the man behind the words, a man with...