The question must be asked: Why another biography of H.L. Mencken? Are there not, already, five substantial biographies of the fabled journalist and critic -- including a major work published in 1994, after researchers were given access to private papers kept sealed for decades after Mencken's death?

Are there not, also, Mencken's five volumes of memoirs -- his three rollicking Days books and two examining his life as a newspaperman and magazine editor -- not to mention sundry monographs on aspects of his work?

What more can there be to say?

Plenty, it turns out.

Terry Teachout's book, The Skeptic: A Life of H.L. Mencken (HarperCollins, 441 pages, $29.95) more than a decade in the making, is a tour-de-force -- easily the most incisive and provocative biography of the man who made his fame as a columnist for Baltimore's Evening Sun and editor of America's premiere literary magazines.

Teachout's life of Mencken distinguishes itself from the two existing biographies held in highest regard -- Carl Bode's Mencken (1969) and Fred Hobson's Mencken: A Life (1994) -- in three important ways.

It is less a chronicle of Mencken's life than an exploration of his mind and character. And Teachout, himself a distinguished journalist, offers more searching analysis of Mencken's work as a newspaperman, author, literary critic and magazine editor. To top it off, Teachout -- whose work, it must be noted, often appears on these pages and whose acknowledgments include The Sun's book editor -- is a vastly more engaging writer than his predecessors.

This combination produces a lively and unvarnished portrayal of a complex and fascinating figure. It will, no doubt, leave many Mencken fans rethinking the man and his work.

Born in 1880, Mencken began his newspaper career just after the turn of the century and kept working until 1948, when a debilitating stroke left him to live out his days unable even to read. In the 1920s, mainly through his coverage of the Scopes Monkey Trial and his work for the Smart Set and American Mercury magazines, he became the most famous and feared journalist in America. In the decades afterward, as he relentlessly attacked Franklin Roosevelt and his New Deal and grossly underestimated the gruesome possibilities of Hitler, his popularity waxed and waned.

But interest in Mencken has never subsided. Before his death in 1956, he had been the subject of three biographies -- all heavily influenced by him -- Isaac Goldberg's The Man Mencken (1925), Edgar Kemler's The Irreverent Mr. Mencken and William Manchester's Disturber of the Peace: The Life of H.L. Mencken (both 1950).

It wasn't until 1969 that Carl Bode published what has become the standard life of Mencken. Exhaustively researched and meticulously documented, Mencken provides as complete a chronicle of his life as any reader could want.

But, in the end, it suffers from two flaws. Bode, an academic, is a dull writer, and his book is more an outline than an exploration. That is particularly disappointing given that readers might have expected more insight from a man who was able to interview scores of people who knew and worked with Mencken.

Three decades later, after the release of Mencken's long-sealed private papers -- among them his explosive diary and the two book-length chronicles of his career, My Life as Author and Editor and Thirty-Five Years of Newspaper Work -- Fred Hobson would build substantially on the foundation laid by Bode.

Hobson, whose book is a far better read, set ambitious goals for himself. He sought to provide the same exhaustive chronicle of Mencken's life as Bode. He wanted to add thoughtful criticism of Mencken's work. And he wanted to explore the thorny issues arising from Mencken's unsealed private papers -- most importantly what Mencken had written about blacks and Jews, which caused a firestorm when the diary was released.

That is a lot to ask of a one-volume biography -- even one that weighs in, notes and all, at nearly 650 pages. It would take twice as many pages to do both subjects justice.

To complicate matters, Hobson equivocates when he needs to be bold. His tendency is to lay the facts on the table and examine them from every angle, but without coming down squarely on one side or the other.

As a result, even though readers may know every detail of Mencken's life, the portrait of the man and his accomplishments never comes as sharply into focus as it does in Teachout's book.

The reason is that Teachout takes a different and more satisfying approach. He makes it plain from the outset that he is writing "a life of Mencken, not the life." That frees him to skip over many of the excruciating -- often uninteresting -- details that weigh down the Bode and Hobson biographies.

Instead, in a slimmer and vastly more interesting book, Teachout is able to devote his attention to providing more penetrating insight into Mencken -- as a writer, editor, thinker and man -- than either of his predecessors.

He recognizes Mencken's unparalleled skill as a journalist, his remarkable work on The American Language and a New Dictionary of Quotations and his masterpieces of style, Happy Days and Newspaper Days.

But he also concludes that much of Mencken's social criticism amounted to nothing more than a "Punch-and-Judy show," and that he was, in many ways, a lousy editor who ran roughshod over writers and published magazines that were often dull.

He points out that Mencken's relentless attacks on those he considered his intellectual inferiors -- the nation's Puritans, pedagogues and Babbitts -- helped liberate American culture, especially literature.

But he also demonstrates that Mencken's philosophy was often contradictory or poorly thought out, and that the man who edited the nation's most influential magazines of ideas showed astonishingly little interest in the artistic and cultural developments of his era.

He shows readers the Mencken who is gregarious with friends, devoted to his mother and brother and tender with his wife.

But he also deals frankly with the man who was a radical in public and a Victorian in private, who judged colleagues "mercilessly" in his diary and who was, without equivocation, an anti-Semite.

It is undeniable that Bode and especially Hobson cover ground Teachout leaves untouched. One important example is that Hobson explores Mencken's attitudes toward African-Americans, which Teachout glides over.

But the bottom line is that Teachout understands Mencken better than any other biographer -- so much so that, in retrospect, it is surprising that Hobson didn't make better use of all the new material available.

Equally important, the Mencken of Teachout's biography is a real man -- warts and all -- not an icon. Biographers tend to choose subjects they admire, and too often that colors their work.

Teachout manages the difficult trick of admiring the traits that made Mencken great -- his incomparable work ethic, his lively mind, his gorgeous prose style -- while being unfailingly honest about his shortcomings.

There was, as Teachout puts it so aptly, "nothing small about him, not even his flaws."

In the end, Teachout offers an assessment of Mencken that rings true: "He was to the first part of the twentieth century what Mark Twain was to the last part of the nineteenth -- the quintessential voice of American letters. Perhaps even a sage, of sorts, too, though an altogether American one, not calm and reflective but noisy as a tornado; witty and abrasive, self-confident and self-contradictory, sometimes maddening, often engaging, always inimitable."

This will not be the last biography of Mencken -- another is already in progress -- but Teachout has set the bar extremely high for writers who come after him. Indeed, with his penetrating insight into the man and his work, Terry Teachout may already have had the final word on H. L. Mencken.

Stephen R. Proctor is the Sun's deputy managing editor for features and sports. He has worked for The Sun for 22 years, and for his entire adult life has been a serious student of the history of this newspaper and The Sun's most famous writer.