Free thinker

Mencken: The American Iconoclast
By Marion Elizabeth Rodgers
Oxford University, 662 pp., illustrated, $35

The hero of Ernest Hemingway's ''The Sun Also Rises" noted his impact. ''So many young men," says Jake Barnes, ''get their likes and dislikes from Mencken." Walter Lippmann, in the Saturday Review of Literature in 1926, called H. L. Mencken ''the most powerful personal influence on this whole generation of educated people."

Henry Louis Mencken never went to college and lampooned ''chalky pedagogues" haranguing ''simian sophomores." When he was city editor of the Baltimore Herald, a reporter asked for a raise, pointing out that he had a BA degree. ''B.A.? Believe Anything, eh?" Mencken responded.

He was amazingly prolific, a blogging phenomenon before the term was invented. A student of the American language, he might have liked the phrase, but would have urged bloggers to stress information over attitude. His style combined relentless facts, a disdain for cliches, and uncompromising integrity. In other words, he was a nightmare for media marketing experts. An editor like Mencken would confound most graphics and demographics consultants. When he took over Smart Set magazine in 1914, Mencken proclaimed as its slogan ''One Civilized Reader Is Worth a Thousand Boneheads." He promised readers ''a moderately intelligent and awfully good time" and kept that promise.

In these parlous times, when ''media personalities" parrot partisan talking points, a visit with Mencken is a seidel of cold pilsner on a hot day. Born in 1880, he died in 1956. Why do people still talk about him 50 years later? The most exhilarating way to find out is to read ''Mencken: The American Iconoclast," by Marion Elizabeth Rodgers. This biography, the best ever on the sage of Baltimore, is exhaustive but never exhausting, and offers readers more than moderate intelligence and an awfully good time.

Edmund Wilson called Mencken a writer of authentic genius. One of the 20th century's best reporters, he diligently harvested facts ''before newspaper reporters were publicists and confidantes of the eminent." He covered presidential nominating conventions from 1904 to 1948, and spoke from experience when he called a convention ''as fascinating as a revival or a hanging." He had covered all three. His editing and reporting animated his lifelong crusade, conducted with gusto, against censorship.

Still, with bookshelves groaning with Menckeniana, why another biography? The author answers that question with extraordinary diligence and insights that avoid both debunking and hagiography. Her reporting is relevant because Mencken's skepticism is needed today in the debate over ''intelligent design," the anti-Darwinian impulse on display in 1925 in the Tennessee town of Dayton, where a schoolteacher, John T. Scopes, was on trial for teaching truth. The special prosecutor was William Jennings Bryan, a three-time Democratic presidential nominee, whose courtroom speech Mencken described for readers of the Baltimore Evening Sun as ''meandering, feeble and downright idiotic." In the 1950s, Mencken entered popular culture in the play based on the Scopes trial, ''Inherit the Wind." His wisecracking reporter was played on Broadway by Tony Randall and in the 1960 film by Gene Kelly.

In a three-volume autobiography, Mencken was such a beguiling memoirist that his version of his life misled biographers. Of the 52 lively chapters in ''Mencken," the most startling is ''The German Valentino," which provides details on the courtly but rakish cherchez-la-femme H. L. Mencken. In 1918, Mencken published ''In Defense of Women," a book that would frustrate today's thought police and paladins of political correctness. Was it sympathetic or misogynistic? Either way, this volume confirmed his status as America's crustiest hard-shell bachelor.

''In his memoirs," Rodgers writes, ''he deliberately concealed the fact that throughout his adulthood he maintained a stable of devoted girlfriends." Some were famous: the playwright Anita Loos, the movie star Aileen Pringle, the Washington writer Gretchen Hood. When Mencken was in his 40s, he finally chose Sara Haardt, from Alabama, the heart of what he called ''the late Confederacy" and, in a notorious essay on Southern culture (or lack of it), ''The Sahara of the Bozart." Haardt was a writer and teacher at Goucher College, also the alma mater of Rodgers, who found in its college library correspondence between the two. Letter writing was one of his blogging skills, says the author: ''Mencken composed at least 100,000 letters in his lifetime, an average of 1,500 or more a year." In those letters, as in every book review, essay, and newspaper story he ever wrote, Mencken's writing style was brilliantly inconsistent. As he explained, ''The main thing in it is rhythm, but it must always be irregular rhythm, never a steady beat."

Mencken's matrimonial bliss lasted for five years before Sara died of pneumonia at 37. In his grief, he went to Europe, after telling friends, ''What a cruel and idiotic world we live in!" He never remarried.

In Germany, Mencken's sentimental fondness for the land of his ancestors overcame his political judgment in what Rodgers calls his ''stupefying naivete about Hitler and his ultimate aims." Although he called the Nazi dictator a ''maniac" and ''preposterous mountebank," she notes, ''he continued to see him basically as a 'buffoon' and essentially harmless." His fondness for Teutonic traits led him to regard Germans as immune to the menace they had democratically chosen. Mencken's language on Hitler echoed what he said about American politicians. Herbert Hoover, for instance, was ''a fat Coolidge," and Franklin Roosevelt was too eager to censor news in wartime, as was his predecessor ''the Archangel Woodrow" Wilson in World War I.

Beyond politics, Mencken and George Jean Nathan, editing Smart Set and the American Mercury, published and encouraged some of the great names in British and American literature: James Joyce, T. S. Eliot, Theodore Dreiser, Sinclair Lewis, F. Scott Fitzgerald, Richard Wright, and even Dashiell Hammett, whose early detective stories they ran in their financially successful pulp magazine, Black Mask.

The book begins in 1926 in Boston, then America's capital of book banning. Mencken defied the Watch and Ward Society, backed by Protestant and Catholic politicians with censoring ambitions, and helped make ''Banned in Boston" an escutcheon of high honor. American liberty also began in Boston, and Mencken was one of its greatest friends. His foes, as this biography gleefully documents, were those who honored American Puritanism, which he defined as ''the haunting fear that someone, somewhere, may be happy."

Martin F. Nolan is a former editorial page editor of the Globe.