At the age of twenty, Andersson debuted with his cartoons in the Söndags-Nisse magazine, where he soon got employed. Inspired by the early comic artists from the United States and England in the late 19th century, Andersson created Sweden's first recurring comic strips: Bröderna Napoleon och Bartholomeus Lunds från Grönköping Resa Jorden Runt (about two brothers on a world tour), Mannen Som Gör Vad Som Faller Honom In (about a strange man who does whatever comes to his mind) and Urhunden (about a prehistoric dog and its owner), all around the turn of the century.
In 1906, O.A., who apparently suffered from long depressions and obsessive-compulsive disorder committed suicide. The reasons for this are not entirely known, but during his work as a reportage cartoonist with the military he was exposed to severe mistreatment of military horses, which as an animal lover worsened his depression.
"Mannen som gör vad som faller honom in", a cartoon by Oskar Andersson.