I don't have a source at hand, but I remember reading an interview where Stieg Larsson confirmed both influence of Pippi and that Mikael Blomkvist was inspired

I don't have a source at hand, but I remember reading an interview where Stieg Larsson confirmed both influence of Pippi and that Mikael Blomkvist was inspired by and named after Astrid Lindgren's character Kalle Blomkvist (translated to English as Bill Bergson).