Bill Bergson (original Swedish name: Kalle Blomkvist) is a fictional boy detective created by Swedish writer Astrid Lindgren.
Lindgren's detective story is of Bill Bergson, a more-or-less ordinary Swedish boy with an extraordinary fascination for detective work. He identifies clues, investigates enigmas, and solves the riddle surrounding a mysterious stranger while the police and other adults overlook or dismiss the whole matter, which results in him and his friends several times solving real crimes including murder and kidnapping. Lindgren wrote shorthand for Harry Söderman, a doctor in Criminology and it was during this work that she learned the basics of criminology that she later used in her stories.
Bill and his friends also play a game they call the Wars of the Roses. He, along with his two friends Anders and Eva-Lotta, are the White Rose, while three other kids, Sixten, Jonte and Benka, are the Red Rose. They "fight" over the possession of Stormumriken, an oddly-shaped stone. The group that doesn't have the stone must use all their wits and energy to obtain it. The group that has the stone must give the other group clues on where to find it.
Although there is a "war" between the two roses all six of the youngsters are good friends and there is simply a playful rivalry between them. The Red Roses help the Whites when they are threatened by real dangers.
Lindgren wrote three books about Bill Bergson:
The character Mikael Blomkvist in Stieg Larsson's Millennium Trilogy is dubbed "Kalle Blomkvist" by the press to mock him in his investigative reporting.