Now, an even more extraordinary part-biography of an equally turbulent composer has just appeared: Henry-Louis de La Grange's Gustav Mahler - Vienna: The Years of Challenge (1897-1904) is the fruit of half a century's fascination with the revolutionary Austrian.
It opens with Mahler's appointment as director of the Vienna State Opera in 1897, and closes with the completion of the Kindertotenlieder seven years later. Through 700 pages of dense but engaging narrative, not a concert, not a row, not a review, not a note is missed. The writing is of an almost scientific exactitude, though the author's passion for his subject rarely wanes.
The second volume in a projected series of four, The Years of Challenge continues one of the most remarkable biographical ventures in the late 20th century. Volume 1, which took Mahler up to 1902, actually appeared in 1974, but has long been out of print. And its author - a slim, boyish- faced 71-year-old of French-American extraction - does not regret its scarcity: "Sometimes I wish it didn't exist at all. I'm so conscious of its weaknesses. It was a pioneer job, written against the clock."
What he calls "Vienna 2" (Vol 3) will appear in 1997, followed by "New York" (Vol 4), covering Mahler's final years. That's where complications arise. "I haven't found a translator yet," he says. "So if you know of a good one...''
For, in fact, the whole biography has already existed for 10 years - in French. And once he has found a translator for what will be OUP's Vol 4, De La Grange will return to Vol 1, and completely revise it - in English. "English was my mother's language. The book was contracted, in 1961, for an English public; and it wouldn't have been conceived at all if I wasn't half-American."
De La Grange lives in Paris, and writes most naturally in his father's native tongue. But he attributes his urge to embrace Mahler so voluminously to his "pragmatic American'' side.
His father, Amaury de La Grange, scion of an aristocratic family related to Empress Josephine, was a French aviator. After working for the French Government at the start of the war, he was imprisoned in Germany for two years by the Gestapo. "Needless to say," recalls his son, "they were terrible years."
Henry-Louis was born in 1924. His mother, Emily Sloane, was the grand- daughter of a Scot who founded a Fifth Avenue furniture store at the start of the 19th century. She used to talk of the operas she went to at New York's Met. She was 20 at the time, and her son realised that she must have heard Mahler conduct. "But she didn't really remember him."
De La Grange was sent from Paris to study in New York just as war broke out. He stayed there until 1941, and then returned from Paris after the war was over. That year saw the first major event of his musical life.
"December: 1945. My parents had rented an apartment on 57th Street, on the same sidewalk as Carnegie Hall. The day we moved in, I went to check the concert posters. Bruno Walter was conducting the New York Philharmonic. I hardly looked at the programme, I just wanted to hear Walter. So it was that I found myself listening to Mahler's Fourth that very night."
Mahler was barely played in Europe at the time. In America, his music was still suspect. De La Grange did not fall instantly in love. "I thought it was scandalous music. How could one write a symphony which sounded neo-classical at a time when neo-classicism didn't exist? It also seemed incredible to have a Lied as a finale. This was not done."
But Mahler's spell had worked, albeit unconsciously. At Yale, De La Grange was soon listening to any recordings of his works he could get hold of. Back in France in 1947, he now knew he wanted to devote his life to music - he studied for five years with Nadia Boulanger - and, above all, to Mahler.
"To me he was a kind of guru. And the more I go on in life, the more I see that he has been that for many people. As a man, he fascinated me - his philosophical concerns, his faith, his pantheism. But ultimately, it is the music that is most important to me, music which unfolds like the evolution of themes and characters in a novel."
The book which he first conceived in the 1950s, and never intended to be so massive, received a crucial boost in 1952 - "the second most important date in my life" - when he met Mahler's widow, Alma, in New York. "She was very kind to me, though she always gave me too much to drink; and she herself drank far too much ever to be drunk. It was obvious that Mahler had been the great man for her, though she never said as much. For me, it was enough to be in her presence, a direct link to him.''
She allowed him to photograph all Mahler's letters to her. Today, these letters are inaccessible, the property of a collector who believes they could lose value if shown. In fact, Alma published them in one of her own books: they cover her time with Mahler, and often reflect his anxiety over her attractiveness to other men. The worst of his fears came true in 1910, when Alma's affair with the architect Walter Gropius caused the composer more pain than any other incident in his life. "Alma says he sometimes lay down in his composing hut in Toblach [in the South Tyrol], so as to be in contact with the earth, because he was suffering so much."
Such images of Mahler roll out one after the other in De La Grange's old-fashioned, French-tinged English - this one, appropriately enough, the day after the BBC National Orchestra of Wales under Mark Wigglesworth had given a stunning rendering of Deryck Cooke's performing version of the unfinished 10th Symphony at the Amsterdam Concertgebouw. It was the 10th on which Mahler was working when the Gropius affair felled him.
Wigglesworth recently visited De La Grange in Toblach, where he now spends every summer. He gives his own image of Mahler's biographer: "He is as close as you can get to Mahler. He is tireless and infectious, surrounded by bizarre faxes up there in the mountains. He is essential for anyone of my generation for whom Mahler is important."
So how has De La Grange sustained this love over so many decades? "That's easy," he answers. "I can hear hundreds of times the same symphony and still notice things I hadn't before. It's what I've called the 'infinite' in Mahler. He has never ceased to stimulate me, and I will never know all of Mahler's music. Whatever I have found or read or discovered, there will always be more."
n 'Gustav Mahler Vol 2' is published this week by Oxford University Press at pounds 30