The pseudonym John Kellermann is used by the co-writers Dr. Georg Friedrich Doll und Stefan Loipfinger.
Dr. Doll studied business economics and is the author of several non-fiction books. He was employed in the industrial and banking sectors for many years. For the last decade heâ€™s been a consultant. He lives and works in Hamburg.
Stefan Loipfinger is a freelance economics journalist and a funds and investments specialist. The recipient of the Helmut Schmidt Journalism Award and the author of numerous non-fiction books, he has also been distinguished for consumer-friendly reporting. He lives and works in Bavaria.