As a conductor, he embraced the contemporary and avoided vacuous maestro worship. Photograph by Jean-Philippe Charbonnier / Gamma-Rapho / Getty

In the wake of the Second World War, a phalanx of young composers took hold of European music, determined to discard a compromised past and remake their art. Chief among them were Karlheinz Stockhausen, Iannis Xenakis, Luigi Nono, Luciano Berio, György Ligeti, and Pierre Boulez. They were in their late teens or early twenties when the inferno ended, and they bore scars—some physical, some psychological—from what Europe had endured. Boulez, who died on January 5th, at the age of ninety, never reached the front lines, but he exemplified the ethos of his generation. Cool, brutal, elegant, fiery, he established a kind of International Style in music, and propagated it in polemical writings and through institutional networks. As a conductor, he was an exacting, absorbing interpreter of the advanced styles he favored. His death marks the end of an epoch: all those revolutionaries of the mid-twentieth century are now gone.

After Arnold Schoenberg’s death, in 1951, Boulez wrote a rather cruel article titled “Schoenberg Is Dead,” in which he said that the modernist master had lost his way in later years and should not be mourned with “pointless melancholy.” It would be antithetical to Boulez’s spirit, then, to offer nothing but banal praise at his passing. He was brilliant, and he was also infuriating; his pugilistic politics did not always serve his cause. The ferocity of his opinions—at one time or another, he found fault with Schoenberg, Stravinsky, Copland, Shostakovich, Britten, Verdi, Tchaikovsky, and Brahms, not to mention a great many contemporary figures—was hardly surprising in an active composer; artists almost require such animosities to clear the air for their own work. It was more troubling in a music director, an administrator, a mentor to young musicians. And Boulez frustrated not only those whom he deemed insufficiently radical but those whose experiments went too far.

When I first read Boulez’s writings, with their often coercive tone (“Any musician who has not experienced—I do not say understood, but, in all exactness, experienced—the necessity for the dodecaphonic language is useless”), I formed a dislike of their author. As I grow older, and begin to wince at my own younger self, I am less inclined to take offense. Boulez fought harder than anyone for the cause of contemporary music, and even those who received his barbs benefitted in one way or another from his energy. No composer of the past hundred years achieved such worldly power: in Paris, IRCAM, the Cité de la Musique, and the new Philharmonie stand as his monuments. In more than one way, he resembled Wagner. He forced you to take sides; his rage was clarifying.

What sort of man was he? Those who knew him in his later years emphasize his charm, his wit, his slyness, his generosity toward like-minded colleagues. This twinkly, avuncular figure is hard to square with the savage youth whom Messiaen, his teacher, described as a “lion who had been flayed alive.” Boulez’s personal life was almost entirely invisible. Several publications identified him as gay, and he was said to have had a tempestuous affair in his youth. But he was silent on the subject. A full biography of him would make for riveting reading.

Last year, on a visit to the Philharmonie, I spent several hours exploring an exhibition dedicated to Boulez. It revealed little of his private life, but the variety of work on display—painters who mattered to him, such as Kandinsky and Klee and Bacon; poets who gripped him, such as Mallarmé and René Char; photographs attesting to his collaborations with such theatre artists as Jean-Louis Barrault and Patrice Chéreau—helped me picture the furniture of his mind. Above all, I was transfixed by the sight of Boulez’s minuscule, spidery handwriting, which almost requires a magnifying glass to decipher. This monkish script speaks of endless hours of solitary devotion.

When I heard of his death, I took out a thirteen-disk set of his compositions, “Pierre Boulez: Complete Works,” which Deutsche Grammophon released in 2013. It is evidence of a constantly questing, questioning intelligence; many of his works underwent revision and expansion over years, even over decades. Certain of the large-scale pieces—the “Livre” for string quartet; “Dérive 2,” for eleven instruments—seem uncertain in their structure: the music fascinatingly streams along, but it lacks narrative direction. To some extent, this moment-to-moment logic was Boulez’s chosen aesthetic; he shared with his onetime friend John Cage an interest in open-ended forms. But when he adopts a clearer, blocklike architecture, as in “Rituel in Memoriam Bruno Maderna,” his colors and textures assume an awesome shape.

Curiously, for a man so steeped in instrumental abstraction, Boulez was at his best when dealing with voices. “Le Marteau sans Maître” (1953-55), a setting of poems by René Char for contralto and chamber ensemble, is a work of ominous allure, the singer flitting birdlike within a fluctuating soundscape that suggests clouds forming over chasms. “Pli Selon Pli” (1957-62), an orchestral cycle on texts of Mallarmé, was his most formidable creation: voice and instruments give flesh and blood to an allegedly inscrutable poet. It begins with a chord like the crack of a whip and ends in similar fashion, its circuitous path encircling a cauldron of emotion.

At various times, Boulez planned to write an opera. He hoped to collaborate with Jean Genet, who made preliminary sketches for a libretto in the late sixties. Boulez also spoke of adapting Genet’s play “The Screens,” which is set during the Algerian war, and in recent years he was said to be working on an opera of “Waiting for Godot.” It is tempting to imagine what eruptions and ruminations these projects might have elicited, but they came to naught. Like the utterly different Leonard Bernstein, Boulez was seduced into a conducting schedule that interfered with his creative ambitions.

Yet his legacy as a conductor is vast, and all to the good. He embodied a new kind of career, one tilted toward the contemporary and away from vacuous maestro worship. His lucid approach to classic works of early modernism, particularly the Second Viennese School of Schoenberg, Berg, and Webern, changed how that music is played and heard. Simon Rattle, one of many forward-thinking conductors who received Boulez’s encouragement, described the status quo: “What one heard was only a struggle.” Boulez took away the struggle—the muddiness and the messiness. As if seen through polished glass, the music assumed an unearthly beauty.

Of Boulez’s hundred and fifty or so recordings, I especially prize his hot-blooded Cleveland Orchestra account of “The Rite of Spring” on Sony; his commanding version of the three-act version of “Lulu,” on D.G.; his ruthless reading of Mahler’s Sixth Symphony; and just about every record he made of the music of Ravel, whom he obscurely resembled—two ascetic sensualists in communion. One radiant Sony disk contains renditions of Ra­vel’s “Trois Poèmes de Stéphane Mallarmé,” “Chansons Madécasses,” and “Don Quichotte à Dulcinée,” with Jill Gomez, Jessye Norman, and José van Dam singing. Tacked on is Roussel’s boisterous Third Symphony—an instance of Boulez engaged in uncompromising fun. His ultimate achievement as a recording artist, though, is the video of the “Ring,” filmed between 1979 and 1980 in Bayreuth, in which his lithe conducting provides the perfect counterweight to Chéreau’s convulsive directorial vision.

Through his music, his recordings, and his lingering aura, Boulez will reverberate into the future. What we will not see again, sadly, is the dapper figure on the podium, hands and fingers flicking this way and that, a diagram in motion. One memory is particularly strong: for a lavish presentation of his electronic-instrumental work “Répons,” at Carnegie Hall, in 2003, stations of musicians surrounded the audience, and Boulez managed to give precise cues back over his shoulder, his force field radiating three hundred and sixty degrees. Perhaps no biography should be written: perhaps this magus should be allowed to vanish from the scene—affable, implacable, unknowable. ♦