Now this is a tough one. Is my favourite writer the same person that writes my favourite series? Or do I have a favourite writer who is my favourite because they are fantastic to interact with? Considering all this I will still have to go with one author:
In many ways she shaped who I am today. Her characters where my childhood companions and heroes. Her books are the books that to a certain extent I still turn to when in need of literary comfort. Her books are probably amongst my most recommended books ever. Just last week I recommended The Brothers Lionheart when someone asked for recommendations for books about death. Her books about Mästerdektektiven Blomkvist certainly influenced me when it comes to my love of mystery. Madicken and Ronja taught me to be brave (and probably encouraged my stubborn and independent streaks). Kajsa Kavat provided me with an opportunity to use logic. While Emil taught me about love and Pippi about having fun and being self-sufficient.
Add to all that the fact that Astrid Lindgren was an advocate for the weaker in society in general and children in particular and my absolute hero worship is complete. I doubt anyone will ever de-throne her.