“The Book of Disquiet” was found, in fragments, only after Pessoa’s death. Illustration by Riccardo Vecchio

If ever there was a writer in flight from his name, it was Fernando Pessoa. Pessoa is the Portuguese word for “person,” and there is nothing he less wanted to be. Again and again, in both poetry and prose, Pessoa denied that he existed as any kind of distinctive individual. “I’m beginning to know myself. I don’t exist,” he writes in one poem. “I’m the gap between what I’d like to be and what others have made of me. . . . That’s me. Period.”

In his magnum opus, “The Book of Disquiet”—a collage of aphorisms and reflections couched in the form of a fictional diary, which he worked on for years but never finished, much less published—Pessoa returns to the same theme: “Through these deliberately unconnected impressions I am the indifferent narrator of my autobiography without events, of my history without a life. These are my Confessions and if I say nothing in them it’s because I have nothing to say.”

This might sound like an unpromising basis for a body of creative work that is now considered one of the greatest of the twentieth century. If a writer is nothing, does nothing, and has nothing to say, what can he write about? But, like the big bang, which took next to nothing and turned it into a cosmos, the expansive power of Pessoa’s imagination turned out to need very little raw material to work with. Indeed, he belongs to a distinguished line of European writers, from Giacomo Leopardi, in the early nineteenth century, to Samuel Beckett, in the twentieth, for whom nullity was a muse. The ultimate futility of all accomplishment, the fascination of loneliness, the way sorrow colors our perception of the world: Pessoa’s insight into his favorite themes was purchased at a high price, but he wouldn’t have had it any other way. “To find one’s personality by losing it—faith itself subscribes to that sense of destiny,” he wrote.

The facts of Pessoa’s destiny are briefly told. Born in Lisbon in 1888, he moved to South Africa at the age of seven, when his stepfather was appointed Portuguese consul in Durban. He excelled at English, winning prizes for his school essays, and wrote English verse throughout his life. In 1905, he moved back to Lisbon to study at the university there. After two years, however, a student strike shut down the campus, and Pessoa dropped out.

For the rest of his life, he devoted himself to reading and writing while supporting himself as a freelance translator of business correspondence. He never married, and while biographers speculate about his sexuality—“I was never one who in love or friendship / Preferred one sex over the other,” he writes in one poem—it is possible that he died a virgin. He was involved in several literary enterprises, including a famous magazine, Orpheu, which, though it ran for only two issues, is considered responsible for introducing modernism to Portugal. He published just one book during his lifetime—“Message,” a collection of poems inspired by Portuguese history, which appeared in 1934. He was a familiar figure in Lisbon’s literary world, but when he died, in 1935, at the age of forty-seven, he had no major achievements to his name. It might well have seemed that he had had “a history without a life.”

But Pessoa was to have an extraordinary afterlife, as he prophesied in his poem “If I Die Young”: “roots may be hidden in the ground / But their flowers flower in the open air for all to see. / It must be so. Nothing can prevent it.” Among his belongings when he died was a large trunk, containing more than twenty-five thousand manuscript pages—the product of a lifetime of nearly graphomaniacal productivity. As Richard Zenith, one of his leading English translators, has written, Pessoa composed “on loose sheets, in notebooks, on stationery from the firms where he worked, on the backs of letters, on envelopes, or on whatever scrap of paper happened to be in reach.”

This cache of documents, which now resides in Portugal’s National Library, contained enough masterpieces to make Pessoa the greatest Portuguese poet of his century—indeed, probably the greatest since Luís de Camões, the sixteenth-century author of the country’s national epic, “The Lusiads.” Among the papers, too, were the hundreds of entries that make up “The Book of Disquiet”—but in no particular order, leaving successive editors to impose their own vision on the work. The first publication of the book was in 1982, nearly fifty years after Pessoa’s death. A newly published English translation, by Margaret Jull Costa, is called “The Book of Disquiet: The Complete Edition” (New Directions), and it is based on a Portuguese edition by Jerónimo Pizarro, which came out in 2013. This was the first version that attempted to put all the entries in chronological order, as best as can be established from Pessoa’s dating and other sources.

In addition to the size and the disorder of the Pessoa archive, there is another confounding level of complexity: it is, in a sense, the work of many writers. In his manuscripts, and even in personal correspondence, Pessoa attributed much of his best writing to various fictional alter egos, which he called “heteronyms.” Scholars have tabulated as many as seventy-two of these. His love of invented names began early: at the age of six, he wrote letters under the French name Chevalier de Pas, and soon moved on to English personae such as Alexander Search and Charles Robert Anon. But the major heteronyms he used in his mature work were more than jokey code names. They were fully fledged characters, endowed with their own biographies, philosophies, and literary styles. Pessoa even imagined encounters among them, and allowed them to comment on one another’s work. If he was empty, as he liked to claim, it was not the emptiness of a void but of a stage, where these selves could meet and interact.

In Pessoa’s poetry, three heteronyms were crucial. In addition to the poems he signed with his own name, he wrote as Alberto Caeiro, an untutored child of nature; as Ricardo Reis, a melancholic doctor dedicated to classical forms and themes; and as Alvaro de Campos, a naval engineer and world traveller who was a devotee of Walt Whitman. Each of these personae was assigned a date of birth within a few years of Pessoa’s own, and their mythologies were intertwined: Pessoa once wrote a passage in which Campos explains how Reis was fundamentally transformed by listening to a reading by Caeiro.

Ordinarily, we expect important poets to have a distinctive style, a way of writing that identifies them as surely as a painter is identified by his brushstroke. But the subdivision of his selves allowed Pessoa to have at least four such styles at once. Writing under his own name, Pessoa is terse, metaphysical, sentimental: