“I suppose you think I’m very brazen,” asks Holly Golightly in “Breakfast at Tiffany’s.” “Or tres fou. Or something.” “Not at all,” answers Truman Capote’s retiring narrator.

Capote’s inspiration for “Breakfast at Tiffany’s” was Christopher Isherwood’s “Goodbye to Berlin,” and Holly is sister to his Sally Bowles.

“Do I shock you when I talk like that, Christopher darling?” asks Sally, early on in her friendship with Isherwood’s eponymous narrator. “Not in the least,” says Christopher. He is not impressed with Sally’s act: “If you go to bed with every single man in Berlin and come and tell me about it each time, you still won’t convince me that you’re La Dame aux Camelias – because, really and truly, you know, you aren’t.”

Isherwood is acknowledging that he did not invent the Sally Bowles type, the social climber who trades on her bad reputation, who pretends to be promiscuous out of whimsy, and whimsical out of genius. What he contributed to the distinguished line is the bland young man who is finally able to handle her.

He was criticized for his narrator’s supposedly cold-hearted credo: “I am a camera with its shutter open, quite passive, recording, not thinking.” There was necessity behind this flourish, though: Isherwood was actively gay in Berlin, but it would have been impolitic to write about that lifestyle in the 1930s. Even Capote, writing in 1950, suffered from the same discretion. (Sally, based on a real woman, got her surname from a young gay man, Paul, who would eventually make his own literary and musical reputation.)

But there is more to Isherwood’s voice than circumstantial sexual politics. This is his centennial year, and the Isherwood oeuvre – vast, autobiographical, but never narcissistic – is a Pepys-like history of 20th century bohemian culture, beginning in the shadow of Bloomsbury and ending in yogic California. And, almost all of this work is in print from New Directions or the University of Minnesota Press.

In the 1970s,writing about his youth, when he felt his homosexuality alienated him from “Nearly Everybody,” he boldly admitted that “even if my nature were like theirs, I should still have to fight them, in one way or another. If boys didn’t exist, I should have to invent them.”

Some of Isherwood’s finest moments are angry. He is no passive camera when he declares that Sally Bowles is deluding herself. Elsewhere Isherwood sentimentally wrote that “Most of the young are bored most of the time – if they have any spirit at all. That is to say, they are outraged – because life isn’t as wonderful as they feel it ought to be.”

Isherwood purposefully failed his Tripos in history at Cambridge, contriving to be sent down, away from a pedagogical scene he found “stupid.” He nonetheless became a kind of historian as an author of period pieces, in the best sense of the word, and of several successive periods. When E.M. Forster worried aloud that his gay novel, “Maurice,” to be published posthumously, would be dated, Isherwood declared “Why shouldn’t it date?”

A recently published and very decent collection of Isherwood criticism makes the case, with its title, that there is something called “The Isherwood Century” (University of Wisconsin Press, 293 pages, $21.95). Novelist Edmund White sums up the case:

A friend of W.H. Auden and Spender, he was a Hindu convert who translated the Bhagavad Gita. Just as his “Berlin Stories” created the myth of Germany between the wars, just as his “Prater Violet” is the best novel I know about the movies, his “A Single Man,” published in 1964, is one of the first and best novels of the modern gay liberation movement.

If Isherwood really was a maker of epochs, as Mr. White suggests, he was certainly no hero. He and good friend Auden fled England as World War II began. In “Down There on a Visit” (1962), Isherwood recalls the “days without a morrow” in London, waiting for the declaration of war in 1938. This same mood overwhelms “Prater Violet” (1946). Fear of tightening English authority made him leave: “If the Nazis got over here, I should be terrified of them, of course; but I could never, at the deepest level of my consciousness, take them quite seriously. Not as seriously as I took my first headmaster.”

Isherwood’s early novels depend on the spiteful energy of bad English schoolboys. “All the Conspirators” (1928), his first novel, consists of little but coy dialogue. Its two protagonists rage within their awkward emotionalism, with no good vocabulary for describing themselves, while mother and sisters wait, impatiently, for them to grow up. Later, Isherwood would jokingly suggest that it was “a very very late Victorian novel,” but it is more a very very early Tennessee Williams play.

Isherwood eventually calmed down, gave up on bitterness to become a camera, but found that mode too passive. The subsequent consolidation of personal confidence and voice is evident between the first and second parts of “The Berlin Stories” (1935 and 1939). In the first part, originally published in America as “The Last of Mr. Norris,” the Christopher character takes up with “a most incredible old crook,” Mr. Norris, in real life a man named Gerald Hamilton. Isherwood recalls that he “introduced Wystan, Stephen, and other friends to him, and soon they were all treating him like an absurd but nostalgic artwork which has been rediscovered by a later generation.”

Hamilton himself wrote a memoir, titled “Mr. Norris and I,” which was probably the most legitimate artistic appropriation in all of the 1950s. Isherwood wrote a preface for Hamilton’s book, in which he regretted the callow, disengaged voice of “The Last of Mr. Norris” and called it a heartless fairy tale. How different, then, is his voice in “Goodbye to Berlin,” the second half of the “Berlin Stories,” standing up to Sally Bowles and even trying to nurture her.

Isherwood’s “I-narrator” technique reaches its pinnacle in “Down There on a Visit,” in which the dispassion of the camera has evolved into an ethic of involved objectivity. Constructed as a sequel to “The Berlin Stories,” it ends with an extended story set in California, where Isherwood spent the last 40 years of his life. The narrator, again called Christopher Isherwood, knows everyone in Hollywood, including Paul, an obnoxious, aging gigolo who takes an interest in Isherwood’s Hindu practice. He takes Paul in and actually converts him. Not only is the author’s treatment of mysticism wonderfully low-key – no Herman Hesse, he – the narrator’s asexual attachment to Paul is the most moving of romances in his work.

Paul eventually breaks down, moves back to Europe, and becomes an opium addict. Isherwood visits him, and even offers to try opium once, to share the experience with Paul, who explodes: “Once! One pipe! Or a dozen pipes, for that matter! You’re exactly like a tourist who thinks he can take in the whole of Rome in one day. You know, you really are a tourist, to your bones.” V.S. Pritchett said that Isherwood was the writer who most barely balanced reportage with art, and in a way all of Isherwood’s writing is travel writing. But it is the good tourist’s sense of being alien that makes him receptive to local differences.

In “A Single Man” (1964), Isherwood’s purest novel and, according to many, his masterpiece, he describes individual personalities as rock pools, each “swarming with hunted anxieties, grim-jawed greeds, dartingly vivid intuitions, deep-down sparkling undiscovered secrets.” When the ocean floods the rocks, the pools commingle.

Isherwood never pretended that knowing people is easy. Friendship is his remote, unignorable muse. Talking about himself for once, but echoing Paul, he explained this to a student:

You want me to tell you what I know.
Oh, Kenneth, Kenneth, believe me – there’s nothing I’d rather do! I want like hell to tell you. But I can’t. I quite literally can’t. Because, don’t you see, what I know is what I am? And I can’t tell you that. You have to find it out for yourself. I’m like a book you have to read. A book can’t read itself to you.