In Sweden 1.d4 Nf6 2.c4 c5 3.d5 b5 turned up at the end of the 1920s.
According to Fritz Kaijser, who over the years has been regarded as the Swedish expert in this area, there was an old teacher of our Grandmaster Gösta Stoltz, named Dahlqvist, who started playing this gambit in Sweden.
Not much attention was paid to the variation until [Bruno] Dahlin, a newspaper assistant to Grandmaster Erik Lundin, frequently played the variation during the Stockholm city championship at the end of the 1920s. Whether he, in turn, had obtained the idea from Dahlqvist is not known. Dahlin was not just anybody. His playing strength was so good that he had been Stockholm city champion.
One of Dahlin’s earliest opponents with this opening was Fritz Kaijser himself. Kaijser was curious about the opening and later he introduced it to his colleagues. There were four players who were together and trained at chess: Gideon Ståhlberg, Gösta Stoltz, Stig Lundholm and Kaijser. The training was organized in such a way that thematic tournaments were played. Once there was an idea of making a compilation of the thematic tournaments. Lundholm was the first victim who compiled material on his opening. Kaijser was the next. But harder times came with the Second World War. Chess was not the first priority, so the gambit 1.d4 Nf6 2.c4 c5 3.d5 b5, which was Kaijser’s department, was never finished. We therefore never had the chance to see how the ideas developed over the years. According to his own statement, the move 4…a6 did not occur at the outset, but was an improvement by Kaijser.
(Small changes from comments to the game Aronian-Carlsen, 2007: www.chessgames.com/perl/chessgame?gid=1462048