Had Andrea Camilleri died in his 50s, his obituary would certainly not have been published in the Guardian. His death might have been noted in the cultural sections of the odd Italian newspaper and it would doubtless have merited a substantial article in the journal of Italy’s pre-eminent drama school, the Accademia Nazionale d’Arte Drammatica, where Camilleri was for many years in charge of teaching directing.

The article might have detailed the achievements of an avant-garde, leftwing intellectual who had had a significant influence on theatre and television in Italy while remaining largely unknown to the general public. It would probably have skipped over the fact that, some years earlier, Camilleri had tried his hand at writing historical novels, but given up after meeting with little success beyond the award of an obscure literary prize, handed out by a town council in his native Sicily.

What he managed to achieve subsequently constitutes a beacon of hope to a greying world.

Camilleri was 66 when his first bestseller, La Stagione della Caccia (1992, published in English in 2014 as Hunting Season), appeared, and 68 when he published the first novel featuring the Sicilian detective, Salvo Montalbano, who was to bring him international renown. But that was only the half of it.

Success inspired Camilleri to a frenzy of literary activity at an age when most writers are in tranquil decline. Between 1994, when his first Montalbano story appeared, and his death, at the age of 93, he not only published 30 books detailing the exploits of his grouchy sleuth, but more than 60 others. Even allowing for anthologies, it was an astonishing achievement. There were years when Camilleri, already in his 80s, published eight titles. He was not so much an author as a one-man literary production line.

Only son of Carmelina (nee Fragapane) and Giuseppe Camilleri, he grew up under Benito Mussolini’s dictatorship in the town of Porto Empedocle on the Sicilian west coast. His father was a harbour official who had taken an active part in the fascists’ rise to power. Andrea was expelled from a diocesan school for throwing an egg that smashed on a crucifix, and he went on to complete his studies at a state school. But he never sat his final exams: the second world war was building to a climax and the exams were cancelled because of the imminent Allied landings in Sicily.

Andrea Camilleri with the actor Luca Zingaretti, who plays Montalbano in the TV adaptation of Camilleri’s novels. Photograph: Mimmo Frassineti/AGF/Rex/Shutterstock

Before the war was over, Camilleri had won a place at university. But he dropped out before obtaining a degree. As a young man, in the late 1940s, he had some success as a poet and author of short stories, even getting on to the short list for a prestigious literary award. But by the end of the decade he had found what, for most of his life, he regarded as his vocation – that of a theatre director.

From 1949 to 1952, he studied direction at the Accademia Nazionale d’Arte Drammatica and went on to a successful career. Among other things, Camilleri is credited with having staged the first production in Italy of a play by Samuel Beckett.

In 1957, the year in which he also married Rosetta Dello Siesto, Camilleri joined the recently founded television arm of Italy’s state broadcaster, RAI. He was the executive producer of a string of hit detective series, including Le Avventure di Laura Storm, which broke new ground in the conservative Italy of the 1960s by featuring the exploits of a female investigator who was also a martial arts expert.

Innovation ran like a thread through Camilleri’s life, entwined with a streak of rebelliousness: from his enrolment in the Italian Communist party (PCI) at the end of the war, through his involvement beginning in 1958 with the Centro Sperimentale di Cinematografia (Cinematic Experimentation Centre), to his support for radical leftwing causes and candidates in later life. He was appalled when the party that had started as the Northern League returned to power in 2018 in a new guise as a hard right, populist movement. In an interview with the Guardian, Camilleri said the League’s leader, Matteo Salvini, reminded him of the followers of Italy’s 20th-century dictator, Benito Mussolini, displaying “the same fascist arrogance, the same smug representation of power”.

Even after he found success as a writer of prose, the experimentation continued. He related a story on the musician Daniele Silvestri’s 2011 album S.C.O.T.C.H., wrote a fantasy trilogy, and helped produce a novel jointly with a fellow author of detective tales, Carlo Lucarelli. Their collaboration, Acqua in Bocca (2010 - the title translates loosely as Mum’s the Word), brings together Montalbano, and Lucarelli’s own unconventional detective, Grazia Negro.

In one sense, the Montalbano novels were not at all innovative: Camilleri named his hero after the Spanish author Manuel Vázquez Montalbán, and admitted he had given him some of the traits of Montalbán’s gourmet investigator, Pepe Carvalho. Moreover, Camilleri churned out the exploits of his most popular character in a way that was decidedly more industrial than creative. “All the Montalbano novels are made up of 180 pages, tallied on my computer [and] divided into 18 chapters of 10 pages each,” he once told an interviewer.

But in an important respect, the Montalbano stories were utterly original. What is not apparent to readers of the stories in translation or to the many non-Italian fans of the television series that sprang from them is that they are written in a language of the author’s creation: a blend of standard Italian with Sicilian dialect.

Luca Zingaretti as Inspector Montalbano in the TV series of Camilleri’s novels. Photograph: BBC/RAI

In La Lingua Batte Dove il Dente Duole (2013, literally Where the Tongue Touches the Toothache), a book-length interview with the linguist Tullio De Mauro, Camilleri explained that the idea arose from the circumstances of his father’s death in the late 1970s and inspired him to try out the technique, unsuccessfully, long before the first Montalbano book appeared.

“One day, to distract him, I said: ‘You know, Dad. I’ve thought of a story,’ and I told him the plot of my first novel … My father goes: ‘Why don’t you write it?’” Camilleri replied that he found it difficult to write in Italian, to which his father replied: “And why do you have to write it in Italian?”

To publishers, Camilleri’s linguistic mish-mash, which even non-Sicilian Italians have difficulty in understanding at first, must have seemed like a refined form of literary suicide. The author was no stranger to rejection slips. But over the course of his much-delayed career Camilleri sold more than 10m books. They were translated into more than 30 languages and adapted for a hugely successful television series that has been sold to more than 20 countries. It was Montalbano’s success on screen that turned Porto Empedocle, the model for his beat, Vigata, into a holiday destination for his many fans. So proud was the town of its most famous son’s literary creation that from 2003 to 2009 it called itself Porto Empedocle Vigata.

Camilleri is survived by Rosetta and their three daughters, Andreina, Elisabetta and Mariolina.

• Andrea Calogero Camilleri, director and author, born 6 September 1925; died 17 July 2019