There is surprisingly little about Gerd Mueller on the web but, in design terms, he's certainly been in the right places at the right time.
I don't believe he ever did any significant work for B&O in terms of product design, but he also did a lot of graphic design during the 60s and 70s so maybe he worked for them then.
Anyway, Mueller worked under Dieter Rams at Braun in Germany during the early 1060s and was one of the key designers behind its household product design at the time - he was involved in the development of several of the company's hallmark razors at that time. He was contracted by Lamy to produce a number of pen designs in the 1960s.
Mueller is often described as a "Bauhaus" designer but, as he was only born in 1932, is probably - like Rams - better described as Bauhaus-influenced.