The girl is Lisbeth Salander, a tattooed bisexual waif with autistic tendencies, a profound distrust of all authority, astonishing ability with a computer and no less astonishing physical courage. This unlikely creation, fiction’s most original heroine in many years, has triggered an international publishing phenomenon. “The Millennium Trilogy”, as the three books are known, has sold more than 12m copies around the world; the last volume was published in Britain this month.

The trilogy’s success shows that complex characters, a fast-paced narrative and a dazzling mosaic of challenging plots and sub-plots can keep readers hooked. The books are long and profoundly political. The sinister conspiracy being played out in the dark reaches of the Swedish security services is an important ingredient in the alchemy that has made the books so successful. Swedish writers have extensively explored the frail heart of the Scandinavian social-democratic dream; Stieg Larsson’s cynical realpolitik carries him from the cold war to the present-day murder of inconvenient witnesses.

Tragically, Larsson did not live to enjoy his success. A pioneering investigative journalist, specialising in exposés of far-right and neo-Nazi movements, he was repeatedly threatened. He was editor of Expo magazine when he died of a heart attack aged 50 in 2004-before the first Salander book was published.

His death predictably spawned various conspiracy theories, but his workaholic lifestyle (he wrote the trilogy at night) and the 60 roll-up cigarettes he smoked a day seem the most likely candidates. There is doubtless something of Larsson in Mikael Blomkvist, the trilogy’s out-of-condition editor of Millennium magazine, who enjoys great success with women when not working 16 hours a day.

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