It says something about the brilliance of John le Carré, and the craft of writing itself, that the very first chapter of his very first book is titled “A Brief History of George Smiley.”

Smiley, arguably the most memorable character in modern fiction, emerged fully formed on that first page. He was an officer in the “Circus,” an imaginary version of British intelligence. His wife, Lady Ann, was faithless from the start. The bookish Smiley retreated into his beloved world of German literature even as he was battling deception, betrayal and murder.

The book was a thin, 148-page detective story titled “Call for the Dead,” published in 1961 when the author was just starting his work as a spy for MI6 in Bonn. He chose the pen name John le Carré as cover for his true identity, David Cornwell. He was just 30, and it was a trial book, a novella more than a fully realized novel. But the author must have known that with this character he had found his voice and vocation.

Le Carré’s death Saturday is a moment when anyone who has ever read a spy novel, or tried to write one, should pause to reflect on what his sort of genius involves. Le Carré wrote fiction, inside a fictional identity, but it was always anchored in real life.

The unlikely reason he could describe Smiley with such precision, he explained in his 2016 memoir, “The Pigeon Tunnel,” was that the character was drawn from the very real person of Vivian Green, the rector of Lincoln College at Oxford, a devoted German scholar and enduringly, the man “who gave me by his example the inner life of George Smiley.”

To say that le Carré invented the modern spy novel doesn’t do justice to his achievement. His fiction was so powerful that in the “secret world,” as he always liked to call it, his imaginary names began to take over from real ones. Intelligence officers never spoke about “moles” until le Carré popularized the term; they talked about penetration agents. Surveillance was drab work until he began writing about “pavement artists” like Toby Esterhase, the Eastern European-born character who directs the “Lamplighters.”

And what of Smiley himself, a character so real that MI6 chiefs (and CIA directors, too) must have felt like impostors? The fictional Smiley (especially as portrayed by the British actor Alec Guinness) made real life redundant. How could John Brennan, or even George Tenet, ever hope to compete? Similarly, pity the Russian spy chiefs who tried to inhabit the mythological persona of “Karla,” the chief of “Moscow Center” and Smiley’s Cold War rival.

Le Carré didn’t just invent the characters in the foreground of the spy world. He designed the entire set — the Cold War battlefield that was painted in shades of gray, with the characters haunted by the moral ambiguity of their work. I’ve always thought that this gray wash was overdone: The Cold War was less ambiguous than le Carré’s fiction suggested. One side was a despotic empire that suppressed the most basic human needs and desires; the other was a collection of democracies that, however corrupt and imperfect, sought to enhance human freedom.

That sounds more like good and evil than moral ambiguity. But no matter: Le Carré’s palette became universal. Cold War espionage was a world of gray because he painted it so powerfully in this monochromatic tone.

Betrayal was le Carré’s sublime theme, to which he returned in all his best books. The lies and manipulation that surrounded the British agent Alec Leamas were at the heart of his breakout novel, “The Spy Who Came in From the Cold,” published in 1963. That book ended at the Berlin Wall with one character left to die, a pawn sacrificed in a game le Carré seemed to despise. And yet, even as he wrote the book, he was an MI6 officer, recruiting those very pawns himself.

The spring of deception that wound so tightly in le Carré’s books began with his father, Ronnie, whose magical, demonic personality inhabited all of le Carré’s novels. As he explains in his memoir, Ronnie was “a conman, fantasist, occasional jailbird, and my father. . . . Ronnie’s life was spent walking on the thinnest, slipperiest ice you can imagine.” He wrote: “Evasion and deception were the necessary weapons of my childhood.”

Le Carré worked and reworked these scenes of his father’s flamboyant perfidy, perhaps most memorably in the autobiographical novel “A Perfect Spy.” It’s not my favorite of his books, perhaps because he’s working to conjure his father’s voice, rather than taking dictation from his preconscious as in the other, subtler books.

At his best, le Carré’s art recalled W.H. Auden’s poem “In Memory of Sigmund Freud”: “He wasn’t clever at all: he merely told/ the unhappy Present to recite the Past/ like a poetry lesson till sooner/ or later it faltered at the line where/ long ago the accusations had begun.”

Le Carré’s two best novels, for me, are the ones in which Smiley is most powerfully rendered, “Tinker Tailor Soldier Spy” and “Smiley’s People.” (I am passing over “The Honorable Schoolboy,” the middle volume of the trilogy, a less memorable book, perhaps because the author was writing in the unfamiliar terrain of Asia, rather than Cold War Europe.)

These two novels are the alpha and omega for a spy novelist. “Tinker Tailor” captures the duplicity of the Circus’s golden boy, Bill Haydon, and the anguish felt by a generation of MI6 officers over the betrayal of real-life double agent Kim Philby, not just a fellow officer but one of the club. The plot builds with such precision and momentum that it’s readable, over and over.

“Smiley’s People” is the novel of revenge: The methodical, gut-wrenching way that Smiley takes down his adversary, Karla. It’s the book in which the moral cost of waging the Cold War is most viscerally portrayed. Again, a book to read and reread.

Le Carré’s best plots evolve in such an easy, meandering way that it’s like watching a ball roll inexorably downhill. There are occasional bumps and excursions, but the momentum is irresistible.

Many of le Carré’s later books are less satisfying for me. In such novels as “The Night Manager,” “The Constant Gardener” and “A Most Wanted Man,” international arms dealers, rapacious multinational corporations and American torturers have replaced the Russians as the bad guys. Le Carré’s anti-American tone becomes relentless and worse, for a reader, it becomes boring and overdrawn.

But these complaints are quibbles. It’s like asking why Woody Allen stopped making funny movies, or why Doonesbury got so solemn. No artist wants to repeat himself endlessly, even if that means tacking away from his best work.

As le Carré wrote in his memoir: “You look back at the books you wrote before the searchlight picked you out and they read like the books of your innocence; and the books after it, in your low moments, like the strivings of a man on trial. ‘Trying too hard,’ the critics say. I never thought I was trying too hard. I thought I owed it to my success to get the best out of myself, and by and large, however good or bad the best was, that was what I did.”

Le Carré’s genius was that his reimaginings of people and events have proved more memorable than the real things. A handful of authors have similarly defined the periods in which they lived — Dickens, Tolstoy, Balzac, Flaubert — creators of unforgettable characters and the very air they seem to breathe. It may seem strange to put John le Carré, the man who invented even his own name, in that league, but I suspect that a hundred years from now, readers will make that judgment.