Mikael Blomkvist is an investigative journalist who fights to protect journalistic integrity and the free press. After losing a libel case when he refuses to reveal his sources, Blomkvist fears his career is over, but he works to repair his reputation as a trustworthy reporter. Blomkvist is loyal and honest; he never hesitates to put himself in dangerous situations to help root out the truth. To Blomkvist, the truth is more important to than anything else.
Lisbeth Salander is the unlikely hero of the Millennium trilogy: a short, skinny, antisocial punk and an ace researcher and hacker. Salander has been abused throughout her life—by her father, her doctor, and her lawyer. She has been unjustly institutionalized, raped, mocked, tortured, and framed for crimes she didn't commit. Book 1 reveals very little about Salander's past, though readers learn of her violent rape, her unique code of justice, and her brilliant mind. But in Books 2 and 3 the web of deceit surrounding Salander's past unravels, giving the reader insight into her antisocial tendencies.
Nils Erik Bjurman is Lisbeth Salander's legal guardian; he demands sex in exchange for allowing Salander to access her money. Later, he violently rapes her, believing her to be too mentally challenged to fight back. When she retaliates by blackmailing him with a videotape of the rape, Bjurman spends the next year obsessing about how to kill her. He partners with Salander's father, Alexander Zalachenko, to destroy Salander.
Villainous Alexander Zalachenko, also known as Zala, is Lisbeth Salander's father. He comes to Sweden as a Russian spy, selling secrets in exchange for refugee status; after defecting he takes up a series of criminal pursuits, including human trafficking. He abuses Salander's mother for years before Salander fights back with a Molotov cocktail, which lands her in a mental institution. Now he wants Salander dead.
The wealthy and successful Martin Vanger takes over his family business, Vanger Enterprises, many years after his sister, Harriet, goes missing. At the end of Book 1 readers learn Martin was sexually abused by his father, Gottfried; in turn, Martin sexually abuses his younger sister. After his father dies, Martin follows in his father's serial-killing footsteps and begins murdering Jewish women.
Dragan Armansky runs a security and private investigation firm called Milton Security. He hires Lisbeth Salander, whom he views as one of the best researchers he's ever met. Armansky trusts Salander because her work is flawless, and for this reason he keeps her on staff despite her strange behavior. Armansky has a crush on Salander and is jealous of Blomkvist, with whom Salander has an easy relationship. Nevertheless, Armansky partners with Blomkvist in Book 3 to help prove Salander's innocence.
The hit man Ronald Niedermann is Lisbeth Salander's powerful half brother and foe. Alexander Zalachenko, their father, has been training Niedermann in the family crime business. Niedermann is often described as a blond giant; he was raised in Germany and briefly trained as a boxer. He has a genetic abnormality that leaves him unable to feel pain, making him the perfect hit man. He also suffers from hallucinations.