Who was responsible for designing the BMW logo?

The BMW logo is one of the most distinctive logo designs in the world, though many differ in opinion as to the origins of the logo design. Nobody yet knows who exactly did the logo, except maybe the founder Franz Josef Popp. The main theory of the meaning of the logo is that the white and blue are supposed to be a rotating propeller, specifically a white propeller blade, against a blue sky, though nobody yet can really confirm whether this is true or not.