One of Britain’s best-known authors, John le Carre, has died.

Le Carre was a pen-name for David Cornwell, who was a spy turned prolific espionage author.

He died of pneumonia in Cornwall on Saturday, aged 89.

Johnny Geller, the chief executive of Cornwell’s agency, the Curtis Brown Group, confirmed the death on Monday (Australian time).

“John le Carre was an undisputed giant of English literature. He defined the Cold War era and fearlessly spoke truth to power in the decades that followed,” he said.

“I represented David for almost 15 years. I have lost a mentor, an inspiration and, most importantly, a friend. We will not see his like again.”

Le Carre’s name appeared on dozens of the world’s best-selling books in the past 60 years, including The Spy Who Came In From The Cold in 1963, and the later Tinker, Tailor Soldier, Spy and Smiley’s People.

His books grappled with betrayal, moral compromise and the psychological toll of a secret life. In the quiet, watchful spymaster George Smiley, he created one of 20th-century fiction’s iconic characters – a decent man at the heart of a web of deceit.

For le Carre, the world of espionage was a “metaphor for the human condition”.

Born David Cornwell, le Carre worked for Britain’s intelligence service before turning his experience into fiction.

“I’m not part of the literary bureaucracy if you like that categorises everybody: Romantic, thriller, serious,” he told The Associated Press in 2008.

“I just go with what I want to write about and the characters. I don’t announce this to myself as a thriller or an entertainment.”

His other works included The Russia House, and, in 2017, the likely Smiley farewell, A Legacy Of Spies.

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Many novels were adapted for film and television, notably the 1965 productions of Smiley’s People and Tinker, Tailor featuring Alec Guinness as Smiley.

After university – which was interrupted by his father’s bankruptcy – le Carre taught at the prestigious boarding school Eton before joining the foreign service.

Officially a diplomat, he was in fact a “lowly” operative with the domestic intelligence service MI5 – he’d started as a student at Oxford – and then its overseas counterpart MI6. He served in Germany, then on the Cold War front line, under the cover of second secretary at the British Embassy.

His first three novels were written while he was a spy, and his employers required him to publish under a pseudonym.

He remained “le Carre” for his entire career.

He said he chose the name – square in French – simply because he liked the vaguely mysterious, European sound of it.

John Le Carré in Coumayeur, Italy in 2001. Photo: Getty

His depictions of life in the clubby, grubby, ethically tarnished world of “The Circus” – the books’ code-name for MI6 – were the antithesis of Ian Fleming’s suave action-hero James Bond, and won le Carre a critical respect that eluded Fleming.

Le Carre reportedly turned down an honour from the Queen – though he accepted Germany’s Goethe Medal in 2011 – and said he did not want his books considered for literary prizes.

In 1954, le Carre married Alison Sharp, with whom he had three sons Timothy, Stephen and Simon, before they divorced in 1971. In 1972 he married Valerie Eustace, with whom he had a son, the novelist Nick Harkaway.

-with agencies