I once asked a group of young composers I was teaching whether there was any modern music they didn’t like. More than half of them mentioned Pierre Boulez. I was initially shocked that they could reject such a supreme musical creator of our time, but the fiercely polemical character of the man may have been the reason for their antipathy. After all, it was Boulez who once declared, without a trace of irony, that any composer who did not acknowledge the necessity of Schoenberg’s 12-tone system was “useless”, and who wrote caustic articles such as “Schoenberg Is Dead”, criticising the Austrian composer’s approach just months after his death in 1951.

Many young composers read his writings, but they don’t always know his music. And yet what you might not guess from the polemics is the sheer beauty of his compositions.

Messiaen, who taught Boulez, would say of him that, underneath it all, he was simply a poet. Messiaen also believed it would take a long time for the wider public to really understand Boulez’s music, because it has a very particular and original sensibility.

I knew of Boulez well before I studied with Messiaen in the late 1970s. Growing up in the UK, I watched his superb documentaries on BBC2, directed by Barrie Gavin. Boulez was the BBC Symphony Orchestra’s chief conductor in the early 70s and together they presented a sequence of inspiring programmes about modern music. Works by Stravinsky, Schoenberg, Webern, Berg, Ives, Bartók, Stravinsky, Varèse, Messiaen and Boulez himself were performed, analysed and contextualised. It was the kind of programming that is so sadly missing today, and it had a huge impact on me as a teenager. I also remember hearing him conduct Berg’s Violin Concerto and the Rite of Spring with the National Youth Orchestra at the Festival Hall, London, and at the Proms where he placed a new Ligeti work alongside his own music.

Messiaen would talk with pride of his former student, describing him as a formidable and immense talent, though when young “he was like a flayed lion”. Boulez was indeed a very angry young man.

Boulez conducting the Rite of Spring in 1963. Photograph: Andre LeCoz/Lebrecht

He attacked anything in sight, including those who had taught him, such as René Leibowitz, a Schoenberg disciple who was largely responsible for introducing serialism to Paris. At one point, Boulez even turned against Messiaen, who had done so much to encourage and help him, and it was five years before their relationship was restored.

Boulez grew up in Nazi-occupied France. He was 20 when the second world war ended. The continent had to make itself anew. Messiaen used to describe travelling home on the Metro with Boulez after classes. Boulez would say “Who’s going to put music right? It’s in such a terrible state.”

And Messiaen would reply: “You.” He considered himself from his earliest days to have an almost Napoleonic mission regarding music and its cultural role. His ambition was not only to compose, but to change the attitude of the public, institutions in France and – later – the wider western world with regard to modernism. He initially pursued this aim with a heightened form of ideological dogmatism. The works of the Second Viennese School, and composers such as Bartók and Varèse, were not played at all in Paris in the late 40s; that they are now part of the international concert repertoire is in large part due to Boulez.

As a conductor, his approach to the early modernist masterpieces has had a tremendous impact on the way they are considered by younger conductors and heard by audiences. He made stupendous recordings of hundreds of pieces of music – among them works by his illustrious contemporaries Carter, Ligeti, Kurtág, Stockhausen, Berio and Birtwistle – and has inspired and helped generations of younger composers.

Through the power of his personality, the scale of his reputation and his considerable personal charm, Boulez has made big things happen, way beyond the confines of manuscript paper. Paris’s new concert hall, the Philharmonie de Paris, owes its existence to him, as does the rest of the Cité de la Musique, his own group the Ensemble Intercontemporain and IRCAM, the musical research institution attached to the Pompidou Centre.

In his own music, however, he moved away from serialism, the great rallying cry of his youth, and over the years has further distanced himself from the concept, now viewing it with scepticism. For me, his best compositions are not the ones from his early years but the works in which the foundations of his earlier idiom are treated much more freely and with greater fantasy. I believe that only when he accepted he was fundamentally a French composer did he find his true voice.

… and with Daniel Barenboim at Abbey Road Studios, London, in 1967. Photograph: lebrecht.co.uk

Le Marteau sans maître (1953-57) was a breakthrough. It is a work in which you can also hear the profound influence of extra-European music, above all from Asia and Africa. This radically alters the sonority and the music’s sense of time and direction, as well as its expressive viewpoint and ethos. Boulez was by no means the first French composer to be open to, and ravished by, eastern music – it had already had a transformative effect on the father of modern music, Debussy, and on succeeding generations – but he took it a stage further, and the curious marriage between his already transforming serial universe and the extra‑European world produced a unique style.

For me, his quasi-symphonic portrait of Mallarmé, Pli selon pli – completed in the early 60s – is a greater masterpiece, and the decades that followed produced gem after gem: Eclat/Multiples, Cummings Ist der Dichter, … explosante-fixe … , Sur Incises ... There is no better postwar piece written for orchestra than Notations, his five hyper-elaborate orchestral canvases, all based on very simple serial pieces he wrote for the piano in his early 20s. Arguably the most important composer-conductor since Mahler, Boulez knows the orchestra more intimately than any of his colleagues, and these short, dazzling showpieces have an intoxicating exuberance and elegance.

Boulez has only published around 30 works in his lifetime, the last about a decade ago. The first time we spent an evening together, in the mid-1980s, I asked him if he had any advice for me. He said: “No, except for one thing: write, just make sure you write lots of music.”

Now aged 90, looking back, he perhaps feels he would have liked to have written more. But I suspect he has not had the easiest of relationships with his muse. This is a man with a vastly refined and critical mind. His intelligence is so questioning and extreme, and his aural imagination so sensitive and acute, that composing must have been a taxing experience. The world today doesn’t need huge numbers of pieces, as it did in, say, Haydn’s time. What are needed, surely, are essential statements, singular and unique works. And these he has provided, without question.

With his conducting and recording, his work with orchestras and institutions in Paris, London, New York and Lucerne, Boulez found a balance that worked for him. He loved conducting, and cherished the contact he has had with the Cleveland and Chicago Symphony Orchestras in the USA, as well as the BBC and London Symphony Orchestras here. His closeness and devotion to the Ensemble Intercontemporain, is such that they resemble family. And then there is his revelatory Wagner interpretation in the centenary Ring at Bayreuth. He has achieved more than most achieve in three lifetimes.

Ultimately I think Boulez is a great optimist, despite the shadows that coloured his early years. In the end what he believes is simple: today’s music has to be different from the music of the past.

That’s a natural thing. Western music continues to evolve and transform and change. And those that don’t agree, well … they’re wrong!

• The BBC Symphony Orchestra’s Total Immersion: Boulez at 90 is at the Barbican, London, on 21 March, part of the Barbican’s Boulez at 90 composer focus. barbican.org.uk. George Benjamin was talking to Imogen Tilden.