Roberto Calasso, the Italian publisher, translator and writer whose wide-ranging works explored the evolution and mysteries of human consciousness, from the earliest myths and rituals to modern civilization, died on Wednesday in Milan. He was 80.

His publishing house, Adelphi, announced the death. No cause was given.

Mr. Calasso was a rare figure in the literary world — an erudite writer and polymath and a savvy publisher who was able to reach a substantial readership for books he released through Adelphi Edizioni, the prestigious Italian publishing house where he worked for some 60 years.

As a writer, he produced more than a dozen works over nearly five decades. His writing defied easy categorization, ranging from his first and only novel, “The Impure Fool,” to his reflections on ancient human consciousness, his study of the 18th-century Venetian artist Giambattista Tiepolo, a book about Franz Kafka, books about Vedic philosophy and Indian mythology, and another about the French clergyman and diplomat Charles-Maurice de Talleyrand-Périgord.

His work drew international acclaim, and was translated into 28 languages and published in 29 countries.

Much of Mr. Calasso’s writing stemmed from his lifelong preoccupation with ancient myths and their meaning, and with uncovering the common allegories and narrative threads across cultures, eras and civilizations. Fluent in five modern languages and proficient in three ancient ones, including Sanskrit, which he taught himself, Mr. Calasso was fascinated by the question of how humans create meaning through shared stories.

“His books are about how the anthropology of stories is universal,” said Jonathan Galassi, president of Farrar Straus & Giroux, the publisher of eight of Mr. Calasso’s books.

He was perhaps best known for his vivid and poetic writing on Greek mythology in “The Marriage of Cadmus and Harmony” (1993), which braided together ancient myths into a novelistic, genre defying work of literature, philosophy, psychology and history. It found a wide international readership and was praised by Gore Vidal as “a perfect work like no other” in reimagining “the morning of our world.”

Mr. Calasso later published “Ka,” an exuberant exploration of Indian religion and philosophy, which The New York Review of Books praised for its “ecstatic insight and cross-cultural synthesis.”

“Calasso carved out a new space as an intellectual, retelling myth as true, certainly as true as science,” Tim Parks, who worked with Mr. Calasso on the English translation of “The Marriage of Cadmus and Harmony,” said in an interview. “His implication is always that we are as subject as our ancestors were to the forces that find their names in Zeus or Venus or Yahweh or Shiva.”

In a 2012 interview with The Paris Review, Mr. Calasso spoke about humanity’s search for transcendence, be it through art, nature or religion, as his central intellectual pursuit. “All of my books have to do with possession,” he said. “Ebbrezza — rapture — is a word connected with possession. In Greek the word is mania, madness. For Plato it was the main path to knowledge.”

Roberto Calasso was born in Florence, Italy, in 1941, into a family of prodigious intellectuals. His maternal grandfather, Ernesto Codignola, was a professor of philosophy at the University of Florence and founded a publishing house, La Nuova Italia. His father, Francesco Calasso, taught the history of law at the University of Florence, and his mother, Melisenda Calasso, was a literary scholar and translator.

With the rise of fascism in Italy, his father was persecuted for his anti-fascist views. When Roberto was 3, the family went into hiding after his father was jailed and accused of conspiring to kill Giovanni Gentile, an intellectual who considered himself the founding philosopher of Italian fascism.

In 1954, his family moved to Rome, where Mr. Calasso fell in love with cinema and with Greek and Roman literature and mythology. In 1962, when he was 21, he started working at the newly formed publishing house Adelphi Edizioni, with the promise that it would be a place where editors could “publish the books we truly liked,” Mr. Calasso told The Paris Review.

A decade later, he became editorial director and quickly developed a reputation for his distinctive tastes and his passion for publishing underappreciated writers like Robert Walser and the German poet Gottfried Benn.

“He was always finding writers who hadn’t had their due and he was always good at publicizing them when he published a book,” Mr. Galassi said. “He was kind of a literary magician.”

Adelphi also published translations of literary titans like J.R.R. Tolkien, Vladimir Nabokov, Jorge Luis Borges and Milan Kundera, as well as books on animal behavior, physics and Tibetan religious texts.

To his authors Mr. Calasso was unfailingly supportive, the writer William Dalrymple said. “If he liked a book and admired an author,” he said, “he could be a loyal and powerful ally and would put his full authority and reputation behind it.”

In “The Art of the Publisher,” his reflections on his decades in publishing, Mr. Calasso was diffident about the commercial side of publishing, noting that “publishing has often shown itself to be a sure and rapid way of squandering substantial amounts of money.” He eventually became the president of Adelphi and helped preserve its independence when he bought a majority stake in the company himself, thwarting a sale to the Mondadori Group, a major European media company.

In a 2015 interview with The New York Times, Mr. Calasso described how perceptions of Adelphi sharply varied.

“At the beginning,” he said, “we were considered rather eccentric and aristocratic. Then, when we started to have remarkable commercial successes, we were accused of being too populist. That was curious because we were publishing exactly the same books.”

As both a writer and a publisher, Mr. Calasso described his works as a single, ongoing project.

“He’s almost impossible to classify, because his range of ideas, his range of thoughts, goes so far and wide,” Richard Dixon, who translated five of Mr. Calasso’s books, said in a phone interview. “He often puts together and juxtaposes ideas where the connection isn’t always obvious.”

Mr. Dixon said that shortly after he learned of Mr. Calasso’s death, he received a package from Mr. Calasso with his two latest books, including a memoir about his childhood in fascist Italy.

“Although Roberto could seem quite intimidating, there was something extraordinarily generous and kind about him,” he said.

Mr. Dalrymple said that though Mr. Calasso could come across as an imposing, uncompromising intellectual in public appearances, he was “charm incarnate” at parties.

And the novelist Lawrence Osborne, who worked with Mr. Calasso on the Italian editions of four of his novels, described him as “quietly inquisitive” and a connoisseur of Negronis, which he and Mr. Osborne drank “in stupendous quantities” while talking about literature and Asian culture.

“For me he was the greatest European publisher of his time and one of our greatest writers — an exceptionally rare combination,” Mr. Osborne said. “Moreover, he was a true Florentine deep down, as I always thought, embodying the urbane tolerance and refinement of that city.”

Mr. Calasso is survived by his wife, the Swiss writer Fleur Jaeggy, and two children, Josephine and Tancredi Calasso, both from his previous marriage to the German writer Anna Katharina Fröhlich.

In his book, “The Celestial Hunter,” Mr. Calasso described writing as something akin to the primordial urge to hunt.

“A book is written when there is something specific that has to be discovered,” he wrote. “The writer doesn’t know what it is, nor where it is, but knows it has to be found. The hunt then begins. The writing begins.”

Gaia Pianigiani contributed reporting from Italy