The Adler Primus was designed by Otto Göckeritz, but since you have said that the designer of this Primus (from about 1933) was not generally associated with cars, and Otto Göckeritz was a long time designer for Adler, I must assume that he is ruled out. A person not usually associated with cars was the architect Walter Gropius, who purportedly worked on a couple of Adler Standard 6 show cars in 1930. Although I can find no connection between Gropius and the Adler Primus, the time frame is about right, so: Is the name you are looking for Walter Gropius?