John le Carré, the British author widely regarded as one of the best spy novelists of all time, has died at 89.

His death was announced by Jonny Geller, the CEO of the literary agency Curtis Brown. No cause of death was given, but Geller said it was not related to Covid-19.

“We have lost a great figure of English literature, a man of great wit, kindness, humor and intelligence,” Geller wrote. “I have lost a friend, a mentor and an inspiration.”

Le Carré, whose real name was David Cornwell, was born in 1931 in the British town of Poole. He started his career as a boarding school teacher before becoming a spy for the British agencies MI5 and MI6. He published his debut novel, Call for the Dead, in 1961; the book marked the first appearance of his most famous character, George Smiley, who would subsequently appear in the author’s well-known novels The Spy Who Came in From the Cold and Tinker, Tailor, Soldier, Spy, among others.

He went on to write more than 20 novels, including, most recently, Agent Running in the Field.

Le Carré was remembered by admirers on social media, including MI6 chief Richard Moore, who called him “a giant of literature who left his mark on #MI6 through his evocative brilliant novels.”

And author Gautam Chintamani wrote, “Le Carré was indeed a ‘Titan of English literature.’ If you want to understand the deeds of men of the last century, look no further than Le Carré.”

Michael Schaub is a Texas-based journalist and regular contributor to NPR.