Janne Dahlmann is a managing editor at Millennium.

In the course of The Girl with the Dragon Tattoo, Mikael Blomkvist discovers that he's been giving out secret information to Monopoly, a magazine owned by Hans-Erik Wennerström. Apparently he played a major role in Wennerström's set-up of Blomkvist. When Janne's disloyalty is proven, Blomkvist and company get revenge on him by feeding him false information to then give to Wennerström's people.