STOCKHOLM (AFP).- Maj Sjowall, one half of a Swedish crime-writing couple credited with inventing "Nordic Noir", has died aged 84, her publisher said on Wednesday.

Sjowall, a pioneer of gritty realism and an inspiration to modern crime writers, "passed away today after an extended period of illness," Ann-Marie Skarp, head of publisher Piratforlaget, told AFP.

With her partner Per Wahloo, who died in 1975, Sjowall penned a 10-book series centred on the dour, middle-aged and decidedly unheroic Martin Beck and his team of detectives in Stockholm's National Homicide Bureau.

Books like "Roseanna", "The Laughing Policeman" and "The Abominable Man," featured tightly structured plots packed with realistic details, charting the unglamourous slog and grind of police work.

"Her and Per Wahloo's 10 novels about Martin Beck... will become classics and have inspired, I dare say, all now living authors of crime novels," Skarp said.

Nordic Noir
The duo also penned the series decades before the likes of Henning Mankell and Stieg Larsson made the genre of "Nordic Noir" into a worldwide hit.

"They broke with the previous trends in crime fiction," Henning Mankell wrote in an introduction to the 2006 English edition of "Roseanna". His own Inspector Kurt Wallander series would owe much to Beck three decades later.

Sjowall was "the giant on whose shoulders the titans of modern Scandi crime fiction stand," Britain's Daily Telegraph wrote in 2015, in a story headlined "The couple who invented Nordic Noir".

Both committed Marxists, they went beyond crime fiction, breaking new ground by carrying out a forensic examination of the failings of Swedish society. The modern themes they tackled included paedophilia, serial killers, the sex industry and suicide.

"Through the eyes of Martin Beck and his colleagues, they held a mirror up to Swedish society at a time when the ideals of the welfare state were beginning to buckle under the realities of everyday life," Scottish crime writer Val McDermid wrote in the introduction to the 2006 edition of "The Man Who Went Up In Smoke".

Late night writing sessions
Born September 25, 1935 in Stockholm, Sjowall studied journalism and graphics. She worked as a translator, and art director, and as journalist for Swedish magazines and newspapers.

It was through her work that she met Wahloo, a successful political journalist, in 1961. The two quickly became a couple and had two sons.

Then they decided to launch the Martin Beck series.

After dinner and having put their sons to bed, they would sit opposite each other and write through the night, a chapter each.

"We worked a lot with the style," she explained to The Guardian newspaper in 2009. "We wanted to find a style which was not personally his, or not personally mine, but a style that was good for the books."

Before actually writing, the couple carefully planned their plots, travelling, taking hundreds of photographs, meeting people and drawing maps, Sjowall explained in a Q&A in the first book "Roseanna".

After Wahloo's death from cancer aged 48 in 1975 -- weeks after the last book in the series, "The Terrorists", was published -- she continued working as a translator.

She also collaborated on "The Woman Who Resembled Greta Garbo" with Dutch crime writer Tomas Ross in 1990.

The Martin Beck books have been translated into 40 languages, according to news agency TT, and served as the source material for dozens of movies.

© Agence France-Presse