He is a satanic cartoon, the nightmare we cannot awake from and the clichi we erect against the void he made. He is the black hole in the middle of our blasted century, a figure so weighted down with the allegorical trappings of Evil that his reality seems ungraspable. Adolf Hitler stands at the limit of so many kinds of human understanding -- moral, political, psychological, perhaps even metaphysical -- that he is forever escaping into the gilded glare of the absolute, like the hideous negative of one of those inscrutable saints in Byzantine portraits. "These people must not know where I come from," Hitler said when he learned of an early investigation into his murky origins. "Nobody must know who I am." For half a century, historians have been trying to learn who he was --and there is still no consensus. In "Explaining Hitler," Ron Rosenbaum tries to approach him indirectly, by interrogating the ways that other scholars and journalists have tried to explain Hitler. He hopes to discover, he says, "if not the truth about Hitler, then some truths about what we talk about when we talk about Hitler. What it tells us about Hitler, what it tells us about ourselves."

Few contemporary writers are better equipped to pull off this tricky double task. Rosenbaum, who writes a column of sui generis criticism for the New York Observer and teaches literary journalism at Columbia University, is a rare triple threat: He is a first-rate thinker, a fine reporter and a superb writer. He is also, as this volume proves, in control of a massive body of scholarly work on Hitler. "What I've attempted in this book is to approach not all but certain aspects of Hitler scholarship with the eye of an educated consumer," he writes modestly. In fact, Rosenbaum's ambition -- and achievement -- is considerably larger than that. "Explaining Hitler" is more than a shopper's guide to Hitler Studies. He doesn't offer, or claim to offer, a unified vision of the obscure Austrian corporal who authored the Holocaust and was personally responsible for the deaths of 40 million people. But Rosenbaum clears away -- or at least makes problematic -- a lot of widely held myths, gives clear and logical accounts of the major controversies in the field and, at crucial moments, delivers his own lucid opinions. The portrait that results is in some ways the intellectual equivalent of a cubist painting: It doesn't always look like the Hitler you think you know, but it gives you the tools to see him in a new, deeper way.

Rather than merely synthesizing the views of Hitler scholars, Rosenbaum interrogates those scholars (and is sometimes kicked out of interviews with them for his trouble), sets them rhetorically against each other, meditates on the psychological needs their views might fulfill. From his strangely truncated interview with the battle-scarred Daniel Goldhagen, author of "Hitler's Willing Executioners," to his challenging conversation with George Steiner, author of a provocative -- some believe obscenely provocative -- novel about Hitler; from a sleepless night spent in the "Gestapo Cottage" near Hitler's mountain retreat to a close encounter with the strange, convoluted mind of revisionist historian David Irving, Rosenbaum turns his quest into an engrossing moral, intellectual and personal odyssey.

What really makes "Explaining Hitler" a page-turner is, paradoxically, the very thing that is most problematic about its method: its founding assumption that Hitler is a vast enigma, a White Whale-like mystery to be forever searched for. This assumption creates intellectual and literary suspense -- when will the hidden truth about Hitler, what Rosenbaum calls the "lost safe-deposit box," be found? -- but it also, inadvertently, tilts the book toward so-called Hitler Exceptionalism, the belief that Hitler was not just quantitatively but qualitatively different from all other human beings.

But if Rosenbaum, in the end, reluctantly sides with the Hitler exceptionalists, to his credit he resists mystifying his subject. And if at times one wishes he had pursued only his ambitious original aim of providing "some answer to the question 'What made Hitler Hitler?'" and had not wandered into the fascinating but endless thickets of secondary historiographical interpretation, he pulls off his audacious double mission with energy and a powerful shaping intelligence. Personal without being self-indulgent, erudite without being pedantic, written with passion and a moral engagement worthy of its momentous subject, "Explaining Hitler" is an exemplary work of intellectual journalism, an idiosyncratic classic.

Rosenbaum opens his book with a vivid and haunting scene: his search for the ur-mystery of Hitler, his family origins. "I was ready to give up and go back," he writes. "A surprise mid-autumn thunderstorm had blown out of Russia and was blanketing Central Europe, making the relatively primitive back roads of this backwoods quarter of Austria increasingly impassable." Rosenbaum and his guide are searching for a ghost town named Dvllersheim -- Hitler's ancestral village, which was "literally blasted off the map and out of existence sometime after Hitler annexed Austria. An effort -- some partisans in the controversy contend -- to erase all traces of certain irregular and disreputable Hitler family events that took place there."

Rosenbaum's attempt to find the ruined village, in a blasted landscape still filled with unexploded shells, opens into and metaphorically reflects the attempts by decades of Hitler scholars to unearth those "irregular and disreputable family events." The crux of those irregularities concerns the mysterious identity of Hitler's grandfather, whose name was left off the baptismal certificate of Hitler's father, Alois Schicklgruber -- a gap that has given rise to what Rosenbaum calls the "family romance of the Hitler explainers," the legend that some mysterious stranger, perhaps a Jew, was Hitler's real grandfather.

The most intriguing evidence for the idea that Hitler had Jewish ancestry comes from Hitler's personal attorney, Hans Frank, who claimed, in a memoir he wrote while awaiting execution at Nuremberg, that while investigating a blackmail threat from one of Hitler's black-sheep relatives he discovered that a Jewish family for whom Hitler's grandmother once worked had paid her child-support money for her son. Hitler's father, then, had presumably been fathered by the Jewish family's 19-year-old son -- making Hitler himself one-quarter Jewish.

"It's astonishing how much mischief this one story has caused since it came to light in 1953 ... how many years of research, years of debate have been devoted to untangling the ambiguities embedded in it," writes decades, one of the two great temptations of Hitler explanation lore [the other having to do with Hitler's affair with his niece Geli Raubal and his alleged sexual perversities], tempting because it offers the gratification of a totalizing, single-pointed explanation of Hitler's psychology." The totalizing explanation is simple: Hitler, whether he believed he had Jewish blood or only feared that he might, sought to "prove his purity, his freedom from infirmity, by the unrelenting, uncompromising ferocity of his war against the Jews, exterminating the doubts about the Jew within himself by murdering all the Jews within his reach."

Rosenbaum, who describes himself as having "a predisposition to Empsonian ambiguity and uncertainty rather than the certainties of theory," is suspicious, here and throughout "Explaining Hitler," of one-bullet Hitler theories like Frank's Jewish-grandfather story -- or like the psychosexual theories about Hitler's alleged abnormalities. For many explainers, Rosenbaum observes, "the longing to find a sexual explanation is almost sexual in its intensity." Various writers have asserted that Hitler was homosexual, impotent, syphilitic, that he had a missing testicle or a freakishly underdeveloped or mutilated penis (one bizarre story asserts that Hitler suffered a disfiguring bite while attempting to urinate in the mouth of a goat) and that he engaged in perverted excretory or urinary sexual practices.

Without entirely ruling any of these out (the last two theories seem particularly persistent), Rosenbaum cites Hitler's affair with a young woman named Mimi Reiter, which was apparently successfully consummated. As for the persistent rumors about Geli Raubal, Hitler's niece and by all accounts the great love of his life, who was found shot, an apparent suicide, in his bedroom in 1931, Rosenbaum declines to join those who assert that she killed herself because she couldn't take her uncle's kinky excretory voyeurism anymore, or who posit a correlation between her death and Hitler's subsequent bloodthirstiness. "To deny or doubt that there was some shameful sexual secret at the core of Hitler's psyche does not diminish the mystery of Hitler's soul," Rosenbaum writes.

In fact, one of his motivations for writing the book, he says, was the "remarkable confidence, despite the shakiness of the evidence, of so many schools of explanation." (He hints that anti-Semitism may help explain why there are so many Hitler-explanation stories that involve Jews, whether they appear as ancestors, lovers or doctors: Somehow, a Jew must be to blame.) He is particularly hard on psychoanalysts who are prone to push-button causation theories. For example, he derides renowned Swiss psychoanalyst Alice Miller's breezy assertion that Hitler's evil was caused by the beatings he was given by his father, and holds up for special ridicule her statement, in response to those who questioned Alois Hitler's brutality, "As if anyone were more qualified to judge the situation than Adolf Hitler himself." ("Yes, and who more deserves our trust and confidence?" he dryly responds.)

Nonetheless, Rosenbaum does find something significant in attorney Frank's tale. It reveals, he argues, not the familiar "demonic, Wagnerian mass-mesmerist" Hitler driven to genocide by psychological self-hatred, but a more sordid, familiar, criminal type -- what he calls "the film noir Hitler, the Munich-demimonde Hitler, one whose relentlessly seedy, small-time character has been forgotten if not erased." The real significance of the Frank story is that it's a blackmail story -- in fact, two blackmail stories. Rosenbaum makes much of the fact that when Hitler heard Frank's report, he blandly asserted that not only had the Jewish family's son not impregnated his grandmother, but that his grandparents had in fact blackmailed the Jewish family by threatening to say that he had! "Consider the kind of Hitler who emerges from the Hans Frank story," Rosenbaum writes. "This is a Hitler steeped in the nuances of small-time sleaze, a Hitler who can think both like a blackmailer and like a blackmailer's victim ... Hitler as sleazy con man, small-time crook."

Rosenbaum's embrace of the two-bit-punk Hitler reflects his desire, throughout the book, to knock Hitler off his demonic pedestal, to present him as evil with a small "e." This realistic, demythologizing impulse, however, later runs head on into a fact so monstrous, so seemingly ungraspable that all "realism," all of the orthodox tools of psychology, appear completely useless: the Holocaust. Dazed by the horrific magnitude of what Hitler did, Rosenbaum never entirely succeeds in integrating his vision of an all-too-human Hitler with the unprecedented mass murderer.

This disorientation is understandable. But might it not at least be argued that the man who ordered the murder of 6 million Jews was still nothing but a spiteful grifter -- that his psychology was not essentially different from that of a thousand other sociopathic murderers? And if German anti-Semitism was as deep-seated and far-reaching as Daniel Goldhagen and others have argued, it becomes possible to imagine that Hitler was not that different, in his ideology and even perhaps in his visceral attitude toward Jews, from many Germans. Rosenbaum's resurrection of the currently unfashionable "Great Man" theory of history is commendable and largely justified, but one of its consequences is that he scants historical context.

The only thing that made Hitler different from your garden-variety anti-Semitic criminal, by this argument, was that he had acquired absolute control over an enormous killing machine. This argument, which terrifyingly posits a total lack of correlation between the magnitude of an intention and the magnitude of a deed, may be too horrific for Rosenbaum to contemplate. The idea that the man who killed a million babies might be identical, in moral imagination, will and consciousness of what he had done, to a punk who bludgeoned a drunk to death in an alley is horrible, absurd -- yet is it really inconceivable? The varieties of criminal pathology are endless.

Moreover, the supposed epic ambiguity of Hitler, the failure of experts to agree on much of anything about him, may not be as significant as it appears. After all, all murder is enigmatic. The closer you look at almost any intelligent, cold-blooded murderer, the more complex and enigmatic he will appear. If you were to send a team of world-class historians, psychologists and philosophers into a maximum-security jail and order them to study a given killer for four decades, it seems possible, even likely, that they would come back with a portrait as multifaceted, contradictory and enigmatic as the one that historians have drawn of Hitler. This is not to argue that this hideously reductive theory is the truth about Hitler, or even particularly interesting. But Rosenbaum's failure even to consider it suggests the seductive power of the massive question marks that generations of scholars have erected, like a row of inscrutable totems.

In any case, Rosenbaum's thought-provoking vision of the grifter Hitler of the '20s leads into what may be his book's most original -- and, for a journalist, certainly its most inspiring -- contribution: his tribute to the courageous, long-forgotten German journalists who desperately tried to alert the world to the terrible menace in Munich -- and often paid for their efforts with their lives. In particular, he salutes the reporters and editors of Hitler's bjte noire, the Munich Post (which Hitler called the Poison Kitchen), and the doomed crusade of an unfathomable editor named Fritz Gerlich, whose savagely Swiftian attacks on Hitler were stopped only when storm troopers smashed into his newspaper office, destroyed his last edition and dragged him off to Dachau, where he was murdered. (One of the most haunting tales in the book concerns Gerlich's steel-rimmed spectacles, which "had become a kind of signature image for the combative newspaper man among those who knew him in Munich." Rosenbaum describes how Nazi thugs notified Gerlich's wife of her husband's death by sending her his famous spectacles "all spattered with blood.")

Rosenbaum justly calls the story of these "first explainers" "one of the great unreported dramas in the history of journalism." If "Explaining Hitler" achieved nothing else, its rescuing of these extraordinary men and women from oblivion would earn it a place in Hitler scholarship. In his characteristically terse, muscular prose (Rosenbaum is the master of the staccato sentence fragment, which he throws after the preceding sentence like a fast right hand after a jab), he ends his chapter with an appeal for German journalists "to do justice to the men of the Poison Kitchen, men who brought so much honor to the profession with their courage and investigative zeal." He closes: "And one more thing I believe ought to be restored: their street address. Number 19 Altheimer Eck should become a memorial and shrine to the Poison Kitchen."

Sequestered in the basement of Munich's Monacensia Library, Rosenbaum stared at the headlines that day after day rang out like warning bells from the Munich Post's front pages. "19 Shot in Terrible Political Bloodbath." "Nazi Party Hands Dripping With Blood." "Germany Today: No Day Without Death." The act of reading the paper, Rosenbaum writes, was nightmarish: "There was something about communing with the actual crumbling copies of the newspaper ... issues in which Hitler was a living figure stalking the pages, that served to give me a painfully immediate intimation of the maddeningly unbearable Cassandra-like frustration the Munich Post journalists must have felt. They were the first to sense the dimensions of Hitler's potential for evil -- and to see the way the world ignored the desperate warnings in their work."

The significance of the Post reporters' coverage of Hitler, for Rosenbaum, is that they saw him, first and foremost, as a "political criminal," not an ideologue. "The emphasis on the down and dirty criminality of the Hitler Party [which the Post insisted on calling the Nazis] is a signature of the Munich Post writers' vision: They were, in effect, enlightened police reporters covering a homicide story in the guise of a political one," Rosenbaum writes. "And, in fact, after immersing myself in their reportage on Hitler and the Hitler Party, I came to see that 'political criminal' was not an empty epithet but a carefully considered encapsulation of a larger vision: that Hitler's evil was not generated from some malevolent higher abstraction or belief, from an ideology that descended into criminality to achieve its aims; rather, his evil arose from his criminality and only garbed itself in ideological belief."

Rosenbaum thus argues that the early Hitler was a political criminal, a murderous grifter. He was possessed by a primitive hatred of the Jews, but he didn't work out a self-justifying ideology until later. Yet Rosenbaum also seems to entertain Lucy Dawidowicz's radical theory that the idea of the Final Solution came to Hitler as early as 1918 (a much earlier date than most historians are willing to posit) and that he never wavered from it. Could Hitler have consciously planned the extermination of European Jewry based only on primitive hatred, without ideology? The idea seems problematic. Whatever the case, Rosenbaum clearly thinks that the cheap-punk Hitler evolved after he took power, turning in some complex fashion into the ideological monster.

But did Hitler really believe in his own ideology? The question of which came first, ideology or criminality, is central to Rosenbaum's book. And it is closely related to an even more primal question: Did Hitler do evil knowing it was evil, like Iago or Milton's Satan, or did he think that what he was doing was "right"? Indeed, do the categories of "evil" and "right" even apply to Hitler's thought-world -- or was he a "moral cretin"? In search of answers to these irreducible ethical questions -- which, as Rosenbaum points out, have been debated by philosophers since at least the time of Plato, who argued in the "Protagoras" that no man consciously does wrong -- Rosenbaum visits two of the towering figures in Hitler explanation, eminent British historians Hugh Trevor-Roper and Alan Bullock, authors respectively of "Last Days of Hitler" and "Hitler: A Study in Tyranny."

On the question of conscious evil, Trevor-Roper has no doubt: "Hitler was convinced of his own rectitude." Much of "Explaining Hitler" can be seen as Rosenbaum's attempt to refute this argument and replace it with a vision of a Hitler who did evil knowing it was evil. Since one of Rosenbaum's guiding theses is that in cases where decisive evidence is lacking, historians, including himself, tend to come up with interpretations that reflect who they are, it is no criticism to say that Rosenbaum's rejection of Trevor-Roper's interpretation seems to be based on moral grounds as much as on the evidence. For if Hitler really believed he was doing the right thing, then in some sense he would be less guilty -- and this is something that Rosenbaum cannot tolerate. He offers the example of the grotesque first Menendez murder trial, in which the brothers were initially acquitted because they supposedly "believed" that their parents were going to kill them. "By that logic, if Hitler had survived to be put on trial for murder in California, say, he might theoretically have been able to argue that he was 'honestly convinced' the Jews were trying to destroy him," Rosenbaum writes.

Rosenbaum suggests that Trevor-Roper has his own understandable reasons for needing to believe in Hitler's sincerity. "Hitler explanations offer contradictory comforts. For [theologian] Emil Fackenheim, it is important to believe that Hitler was insincere and opportunistic precisely because he doesn't want to exempt Hitler from the gravest degree of responsibility, from conscious, premeditated knowing evil. Perhaps for Trevor-Roper, that degree of knowing evil, evil without the fig leaf of rectitude, is inconceivable or unbearable to contemplate."

The argument Rosenbaum makes against Trevor-Roper is powerful, if not entirely decisive. He points out that in the "Table Talk" transcripts, records of Hitler's late-night ramblings, the F|hrer tells SS chief Heinrich Himmler and his top accomplice, Reinhard Heydrich, an obvious and chilling lie, denying that he was killing Jews when in fact all three men knew that the Final Solution was in full swing. "One can imagine the glances that Hitler, Himmler and Heydrich must have exchanged during the orchestration of this elaborate charade for the stenographer, perhaps even the silent laughter." For Rosenbaum, "This is not the language of a man 'convinced of his own rectitude' in exterminating Jews. This is the language of a man so convinced of his own criminality that he must deny that the crime is happening."

Yet, as Rosenbaum himself acknowledges later, "There's nothing intrinsic in the fact of concealment to make it a necessary conclusion that concealment came from shame as opposed to, let's say, 'idealistic' prudence." Hitler, by this logic, might have been aware that the world didn't think slaughtering the Jews was a good thing, even though in his heart he knew it was -- a variant of the "the masses are not yet ready to understand our (Cultural Revolution, Armenian genocide, Rwandan butchery, American slavery, Bosnian atrocities, etc.)" line -- and therefore concealed it.

Rosenbaum's encounter with Bullock deepens the argument -- and reveals that Bullock had changed his mind in a fascinating way about Hitler. In his still-standard 1952 biography, "Hitler: A Study in Tyranny," Bullock had argued that Hitler was a mere mountebank, an adventurer devoid of conviction, interested in power for its own sake. It was a pragmatic, deflating vision of Hitler that stood at the opposite pole from Trevor-Roper's messianic, almost possessed F|hrer. (So powerful was Trevor-Roper's portrait that some thought it glorified Hitler: The Zionist terror group the Stern Gang actually issued the historian a death threat.) Now, however, Bullock had come to see Hitler as "double-minded" -- not just as a cynical actor, but as "the great actor who believed in the part." He cites a passage from Nietzsche: "In the very act of deception ... they are overcome by their belief in themselves, and it is this belief which then speaks so persuasively." In a dark dialectic, calculation becomes sincerity -- but cynicism comes first.

Like Bullock, Rosenbaum thinks that Hitler masked his real feelings, perhaps even transformed them so that they were palatable to him. But rather than seeing cynicism transformed into sincerity, he sees primitive hatred transformed into, or masked by, ironic knowingness -- a mask revealed by "the way he would come to make artful little knowing jests about it, virtually chuckle over the magnitude of his hatred." This "mirthful knowingness," for Rosenbaum, is the true signature of Hitler's unfathomable evil, his ticket to the lowest circle of hell.

Rosenbaum's encounter with one of the most thought-provoking figures in the book, philosopher Berel Lang, takes the analysis still further. For Lang, "Hitler and his cronies raised the consciousness of evil to a veritable art: created ... the art of evil." Lang believes that it was "the role of the imagination in the elaboration of their acts," the "sense of irony" manifest in things like the sign "Arbeit macht Frie" ("Work Will Make You Free") over the gate to Auschwitz -- "it's like a joke, it is a joke" -- that indicate "an artistic consciousness" in evil. Which is to say that Hitler and his cronies did what they did not in spite of the fact that they knew it was wrong, but because they knew it was wrong.

If there is one image of Hitler that Rosenbaum wants to leave us with, it is the image of him laughing -- or perhaps smiling silently -- at the thought of his victims. In a brilliant excursus on the late Lucy Dawidowicz, he invokes three remarkable passages she cites in which Hitler repeatedly refers to the "laughter" of the Jews. "Of those who laughed then, countless ones no longer laugh today," Hitler said, "and those who still laugh now will perhaps in a while also no longer do so." Rosenbaum comments that this speech "is a confirmation of Berel Lang's thesis that it is in the savoring of the slaughter as an aesthetic experience, in the perpetrator's relishing its piquant artful ironies, that the highest degree of conscious evil discloses itself." If in "Explaining Hitler" Rosenbaum at some level is putting Hitler on trial, it is a powerful closing argument for total moral condemnation.

But should one even attempt to explain Hitler? In one of the most shocking chapters in the book, Rosenbaum confronts someone who not only believes that all Holocaust explanation is "obscenity as such," but who imperiously censors those who venture such explanations. If there is an intellectual villain here, it is Claude Lanzmann, director of the acclaimed nine-hour documentary "Shoah." Rosenbaum approaches Lanzmann respectfully, only to be treated with a high-handed disdain that approaches intellectual fascism. As Rosenbaum portrays him, Lanzmann, egged on by his Lacanian acolytes -- lickspittles is more like it -- clearly regards himself as the sole keeper of the sacred flame, and has ruled from on high that all attempts at explanation of a horror so absolute as the Holocaust are morally obscene, since they might somehow exculpate or lead to understanding of the perpetrators.

One might accept or at least understand this stark taboo in the abstract. But Rosenbaum recounts a damning scene in which Lanzmann, who is not a Holocaust survivor, publicly humiliates and browbeats an actual Holocaust survivor, Dr. Louis Micheels. There could be no more devastating portrait of hubris, abstract rage and Parisian intellectual arrogance.

As he abruptly terminates his interview with Rosenbaum, Lanzmann instructs him to read an essay he had written called "Hier Ist Kein Warum" ("Here There Is No Why"). The title is taken from a line in Primo Levi's memoir, "Survival in Auschwitz." On his first day in camp, Levi, tormented by thirst, tries to break off an icicle hanging outside the window. The guard brutally snatches it way from him. "'Warum?' I asked him in my poor German. 'Hier ist kein warum' (there is no why here), he replied, pushing me inside with a shove."

Rosenbaum writes that he is still astonished that Lanzmann could have put this line to the use that he did. And he gives Micheels, a humble and soft-spoken man, the last word.

The world of Auschwitz, Micheels tells Rosenbaum, "was inhabited by creatures that had little if anything in common with what we consider human beings ... In that world, I agree, 'ist kein warum.' However, in the civilized world to which so few of us, including Primo Levi, returned, there should be -- da sollte ein warum sein. Without an attempt, no matter how difficult and complex, at understanding, that very world, where truth is most important, could be lost again."

"'Da sollte ein warum sein,'" Rosenbaum translates. "There must be a why." His own book, which unblinkingly confronts the hardest of the hard questions our century has faced, is an important part of the answer that will never be given, yet that we must try to give.