Petz, Moritz: - Moritz Petz, alias Udo Weigelt, was born in Hamburg, Germany. Upon completion of his studies, he traveled through Italy, Denmark, and Sweden, working a variety of jobs before returning to study history and German. He has written many books for children including the badger book that started it all: The Bad Mood. Today Udo Weigelt lives as a freelance writer on Lake Constance.