A brilliant, asocial researcher and hacker with a photographic memory and exceptional capacity for pattern recognition. Declared legally incompetent as a teenager following a confrontation with her father Zalachenko, she was institutionalised and subjected to abuse by the state. Fiercely independent, she operates by her own moral code and does not forgive those who harm her or the vulnerable. Bisexual, heavily tattooed, and lives almost entirely off the grid by choice.

Co-owner and publisher of Millennium magazine and an investigative journalist with a reputation for exposing financial corruption. Convicted of libel against financier Hans-Erik Wennerstrom at the opening of the first novel, he accepts Henrik Vanger's commission to investigate the disappearance of Harriet Vanger as a way to find evidence that will clear his name. Principled, persistent, and given to affairs with women he works with.

A Soviet GRU agent who defected to Sweden in 1976 and was given a new identity as Karl Axel Bodin by the Section. Lisbeth Salander's father, whom she attempted to kill at age twelve after years of his abuse of her mother. The Section covered up the incident and had Lisbeth institutionalised to protect their asset. Runs a trafficking operation through Ronald Niedermann.

Lisbeth Salander's half-brother and enforcer for Alexander Zalachenko. A giant who feels no pain due to congenital analgesia. Extraordinarily dangerous in physical confrontations. Kills Dag Svensson and Mia Bergman on Zalachenko's orders in the second book.

Director of Milton Security, a private security firm. Lisbeth Salander's employer and one of the few people she considers an ally. Has a protective, quasi-paternal relationship with Salander. Of Armenian origin, based in Stockholm.

Editor-in-chief of Millennium magazine and Mikael Blomkvist's long-term lover and closest friend. Married to artist Greger Beckman in an open relationship. Calm under pressure, politically astute, and fiercely loyal to both Blomkvist and the magazine. Takes a position as editor of the newspaper SMP in the third book.

Lisbeth Salander's first court-appointed guardian and the closest thing she has to a father figure. A retired lawyer who genuinely cared for her and fought to protect her rights. Suffered a stroke and was replaced by Bjurman. Recovers slowly and returns in the third book to lead her legal defence.

Detective inspector with the Stockholm police who leads the investigation into the murders of Dag Svensson and Mia Bergman in the second book. Initially pursues Salander as a suspect but gradually becomes convinced of her innocence. Methodical and fair-minded, increasingly at odds with the conspiracy within SAPO.

The stocky, capable engineer of the Clear Air Turbulence. Good-natured and practical, Wubslin maintains the ageing ship through its many ordeals. He dies heroically in the Command System, staying at the train controls to try to move it out of the path of an oncoming collision.

Surgeon at Sahlgrenska Hospital who operates on Salander's brain and helps smuggle her a Palm handheld.

Blomkvist's sister, a lawyer specialising in family law and women's rights.

Millennium's new managing editor who replaces Blomkvist in the day-to-day running of the magazine.

Tall, athletic intelligence officer at Constitutional Protection who investigates the Section and begins an affair with Blomkvist.

Angelica's younger brother, a small boy from Cittagazze who is fiercely bold despite his age, boasting of killing Specters and following his sister everywhere.

Psychiatrist who treated Salander as a child at St. Stefan's, keeping her strapped to a bed, and later conspires with the Section to have her declared incompetent.