The hard facts alone are damning enough. When Goebbels set up his Reich Chamber of Culture in 1933, Strauss became president of its music section, and in 1934 publicly praised Hitler's cultural policies. When he was dismissed a year later, he sent Hitler a grovelling telegram begging to be allowed to go on serving him. He composed an Olympic hymn, which he duly conducted in 1936.
In 1938, he helped celebrate Nazi mythology by performing at Goebbels's Olympic-style Reichmusiktage. Until the end of the war he remained the Nazis' prime cultural asset. He did not attack their policies when they were in power, and offered no recantation when they were gone.
Moreover, it seems incontrovertible that his grief over the war's effects was largely reserved for the opera houses destroyed. "I am in despair," he told a friend. "My lovely Dresden - Weimar - Munich, all gone!" His daughter-in-law was Jewish, as was his beloved librettist Stefan Zweig, but the horror of the Holocaust seemed to pass him by. While he was writing his exquisite drawing-room comedy Capriccio, the ovens of Dachau were going full blast just down the road. Strauss felt himself to be above politics.
Here we are on the biographer's slippery slope: I have twice used the word "seem". The truth about this secretive composer's Nazi relationship will forever be veiled in mystery, as four new works marking the 50th anniversary of his death make clear.
For Michael Kennedy, Strauss's Nazi involvement was essentially a "misjudgment", a misguided attempt to salvage what he could from encroaching barbarism. For Bryan Gilliam, the author of The Life of Richard Strauss (Cambridge, pounds 9.95), his involvement was the fruit of "pragmatism, self-interest, expediency". For Matthew Boyden, on the other hand, it was quite simply a "pact with evil".
For Tim Ashley, author of Richard Strauss (Phaidon pounds 14.95), the composer was guilty of "ugly compromise", but his complicity was only skin-deep.
Strauss was not a member of the Nazi party, but was his son? Yes, say Ashley and Boyden; Kennedy insists not. But Kennedy is avowedly partisan. Whenever the facts permit it, he gives the composer the benefit of the doubt. While Boyden sees Salome as "a stridently anti-Semitic opera", Kennedy sees no anti-Semitism at all. You pay your money, and take your pick.
If Gilliam's short book is efficient but undistinguished, Boyden's ought to come with a health warning. It's essentially an indictment, in which guilt-by-association looms large. With liberal use of "probably", "must have known about", and "can have been in no doubt that", this over-zealous prosecution finds virulent anti-Semitism lurking under every stone along the young composer's path.
Boyden is properly responsive to much of the music, but his writing is slapdash, his translation unreliable, and his commentaries sometimes breathtakingly crass. We are asked to believe that the majestically original tone-poems "were consciously addressed to the sympathies of middle-class audiences", and that Strauss wrote Salome to court "avant-garde approval".
No such rubbish mars Kennedy's magisterial book, whose musical authority is in no way weakened by its political special pleading. The genesis of every major work is documented, yet the account is never less than readable. The book is full of significant sub-plots, such as Schoenberg's progression from love to hate, to cautious reconciliation.
Kennedy writes with real insight about Strauss's long marriage to the turbulent Pauline, and perceptively about his lifelong addiction to the German card-game Skat. Strauss composed ceaselessly, whatever else he was doing, and cards were his one relief from the demands of his unsleeping muse.
However, new readers should start with Ashley's short study, which presents the interplay between life and work with persuasive economy. By placing Strauss in the 18th-century tradition of composing-for-patronage, Ashley sounds the right note. His commentaries illuminate, his musical responses are marvellously fresh. By pointing out the impossibility of "apolitical" art under totalitarianism, he pre-empts Kennedy-style exculpation.
With so vivid a tale, it's no surprise that the same key utterances should ring through all these books.
Pauline, on her husband in bed: "What does one do with a man who, when he begins to get sensual, starts composing?" Strauss on his creative urge: "While reading Schopenhauer or Nietzsche or some history book, I will get an uncontrollable urge to go to the piano. Before long a quite distinct melody appears."
The dying Strauss, quoting the dying Isolde: "Greet the world for me".
This man was, like Mozart, truly a slave to music.