Swedish author (1858-1940), perhaps the greatest novelist Sweden has ever produced, and one of the world's greats. Winner of Nobel Prize for Literature in 1909. You can find further biographical information here.
Gösta Berlings Saga. Her masterpiece. A dark saga laced with glimpses of what could be magic, but probably is just darkness in the soul. Rich and complex -- not the unrelenting downer that is Sigrid Undset. The Swedish is difficult, and I did not follow this all that well, but I'm in the middle of re-reading it. There is a wonderful essay on Berling and on Lagerlöf's other work, by Marguerite Yourcenar, collected in The Dark Brain of Piranesi.
En herrgårdssägen. A short and concentrated love story, the most beautiful and unorthodox I've ever read.
Nils Holgerssons underbara resa genom Sverige. Her classic childrens' story of Nils travel with the goose Akka. Not just for kids, of course. Published 1906, ultimately in two volumes.