Harriet Vanger is a fictional character from the Millennium series, created by author Stieg Larsson. She is the niece of Henrik Vanger, a wealthy industrialist, and plays a central role in the first book, The Girl with the Dragon Tattoo. Harriet mysteriously disappears at a young age, prompting a decades-long investigation into her fate. Her disappearance is a key plot point that drives the story forward, as journalist Mikael Blomkvist and hacker Lisbeth Salander work together to uncover the truth. Harriet's character represents themes of trauma and resilience, making her a significant figure in the narrative.