 On July 1, 1945, Müller began working as a self-employed painter and graphic designer in Halle.In 1946, he became a member of the Artists Association of the Democratic Republic of Germany – known in German as "Verband Bildender Künstler" (VBK) – which had been set up by Richard Horn (1898–1989) and Karl Völker.During this period, Müller earned his living by composing advertising materials, cinema posters for example.