He joined the Italian Communist Party at the start of the so-called Years of Lead, a period of political violence and social upheaval in Italy. He justified that decision because the party’s denunciation of the Soviet invasion of Czechoslovakia in 1968 allowed him to square doctrine with democracy. He was escorted from one of his own recitals for protesting the U.S. bombing of Hanoi, and he befriended the composer Luigi Nono, with whom he collaborated on works like “Como una ola de fuerza y luz,” dedicated to the memory of the Chilean activist Luciano Cruz.

Convinced that music was a right for all, Mr. Pollini gave concerts for workers and students with the conductor Claudio Abbado, a lifelong collaborator, and he abandoned conventions that separated new music from old, recording the piano works of Schoenberg as strikingly as he did the late sonatas of Beethoven. His fervor had dimmed by the 1980s — “It was something of a letdown,” he subsequently said of the period — but he retained his socialism, along with an idealistic belief in the power of art.

“Art itself, if it is really great, has a progressive aspect that is needed by a society, even if it seems absolutely useless in strictly practical terms,” Mr. Pollini told The Guardian in 2011. “In a way, art is a little like the dreams of a society. They seem to contribute little, but sleeping and dreaming are vitally important in that a human couldn’t live without them, in the same way a society cannot live without art.”

Mr. Pollini kept up with modern art, read all of Shakespeare repeatedly in English and Italian, and studied scores well beyond those for the piano. But he selected what he performed with care, committing only to works that he knew he would never tire of, and that had contributed to what he saw as the evolution of music.

Even so, Mr. Pollini was a modest modernist. Rarely seen without a jacket, a tie and cigarettes, he spoke of his appreciation for musicians of antithetical persuasions, from the arch-Romanticism of the pianist Alfred Cortot to the regal grandeur of the conductor Karl Böhm, with whom he made exquisite recordings of Mozart, Beethoven and Brahms concertos. Unusual for a modernist, he even confessed to listening to Rachmaninoff from time to time.

Mr. Pollini’s survivors include his wife, Maria Elisabetta, commonly known as Marilisa, whom he married in 1968, and their son, Daniele. Both his wife and his son play the piano.

“We have the most beautiful repertoire ever written for an instrument,” Mr. Pollini said of pianists in an interview with The Times in 2006. “We have at our disposal a richness. And then we deal with an instrument that has an absolutely extraordinary possibility. There are no limits to what you can do on the piano.”