García Márquez’s readers sometimes imagine that supernatural events and folk beliefs in his novels express an all-­purpose spirit of primitivist rebellion, suitable for adaptation by progressive-minded writers in every region of the formerly colonized world. Martin endorses that interpretation in the opening sentence of his biography, where he flatly defines García Márquez, encyclopedia style, as “the best-known writer to have emerged from the ‘third world’ and the best known exponent of a literary style, ‘magical realism,’ which has proved astonishingly productive in other developing countries.” But I think that, on the contrary, magical events and folk beliefs in the writings of García Márquez show how powerfully the Golden Age has lingered in memory. Instead of a post­colonial literary rebellion against Western imperialism, here is a late-blooming flower of the Spanish high baroque. Gongorism disguised as primitivism. And, being a proper son of Darío, García Márquez has gone on to embrace in his mad spirit the glories of Spanish rhetoric at its most extreme.

Martin tells us that in García Márquez’s own estimation, his greatest book is “The Autumn of the Patriarch,” from 1975 — a book that is an extended homage to Darío, who is invoked at the beginning and again at the very end, and who, somewhere in the middle, shows up as a character, sailing into port on a banana boat to deliver a poetry recitation. Every last sentence in “The Autumn of the Patriarch” offers a heroic demonstration of man’s triumph over language — unless it is language’s triumph over man. The sentences begin in one person’s voice and conclude in someone else’s, or change their subject halfway through, or wander across the centuries, and, even so, conform sufficiently to the rules of rhetoric to carry you along. To read is to gasp. You want to break into applause at the shape and grandeur of those sentences, not to mention their length. And yet to do so you would need to set down the book, which cannot be done, owing to the fact that, just when the impulse to clap your hands has become irresistible, the sentence you are reading has begun to round a corner, and you have no alternative but to clutch onto the book as if steering a car that has veered out of control.

Those are gorgeous sentences, but they are also tyrannical — and tyranny, in the conventional political sense, is entirely the novel’s theme. “The Autumn of the Patriarch” tells the story of a despot ruling over an unnamed and benighted Caribbean land. It is a dictator novel. The marriage of plot and prosody makes it a masterpiece — a greater triumph even than Mario Vargas Llosa’s marvelously brilliant “Feast of the Goat,” which is likewise a Caribbean dictator novel, and likewise invokes Rubén Darío. “The Autumn of the Patriarch” does have a puzzling quality, though. The dictator whose portrait emerges from those ­tropical-flower sentences is monstrous and despicable — yet even his creepiest tyrannical traits are presented as signs of the human condition, deserving of pity and compassion, maybe even a kind of sorrowful love. I have always wondered what sort of political attitude García Márquez meant to convey with those peculiar ambiguities.

But now that I have read Martin’s biography, I know. The book is 642 pages long, and the first half of it, after completing the genealogical survey of northern Colombia, records the dreadful poverty that García Márquez and his wife and two sons endured before 1967, when “One Hundred Years of Solitude” finally lifted him into the comforts of multiple-home ownership and, in 1982, the Nobel Prize. But the second half mostly recounts the novelist’s subsequent career as hobnobber among the powerful — a man who, according to his biographer, has labored hard and long to get himself invited to the dinner tables of presidents, dictators and tycoons around the world. And among those many table companions, no one has mattered more to him than the maximum leader of the Cuban revolution, Fidel Castro, with whom García Márquez has conceived a genuine friendship, based on shared vacations, a part-time career promoting Havana as a movie-industry capital and a history of defending the Castro dictatorship against its detractors in the Hispanic literary world. Here is the real-life Caribbean tyrant. García Márquez does lead you to think about Castro in some of those spectacular sentences in “The Autumn of the Patriarch.” And the novelist plainly loves his dictator.

Martin gushes over nearly everything that García Márquez has ever done, yet, even so, he concedes that friendship with Castro has sometimes aroused criticism. The biographer mentions twice that Vargas Llosa (who at one point punched García Márquez in the face, for reasons possibly bearing on marital honor) has described García Márquez as Castro’s “lackey.” Martin emphasizes the insult mostly to show the indignities that García Márquez has undergone out of fidelity to Fidel. And yet, the biography’s account of the friendship will make readers pause thoughtfully over that word, “lackey.” Martin tells us that, on an occasion when Castro visited Colombia, García Márquez volunteered to be one of his bodyguards. The world’s most popular serious novelist does seem to be a flunky of the world’s longest-lasting monomaniacal dictator. Why García Márquez has chosen to strike up such a friendship is something I cannot explain — except to point out that, as Martin shows, the great novelist has never veered from the epiphany that came to him at his grandfather’s house in 1950, and he has always been fascinated by the grotesque, the pathetic and the improbable.