Hiller was a German writer and publicist, known in this period as the editor of the first anthology of Expressionist poets, Der Kondor (1912), which included poems from Werfel; he was also known for promoting what he called literary activism, a perspective with which Werfel took issue in his open letter to Hiller. Georg Müller was a publisher based in Munich with whom Hiller was publishing an anthology.
From the description of Correspondence to Franz Werfel, 1912-1917. (University of Pennsylvania Library). WorldCat record id: 155863458