His first book for young readers, "Kraniche – Kurs Süd" (Cranes – heading south) was published in 1956. His breakthrough came in 1962 with the novel for young adults, "Das Jahr der Wölfe" (The Year of the Wolves). Since then he has published a large number of books for children and young adults. His works have been translated for international readers and have won numerous literary awards. He received the Grand Prize of the German Academy for Literature for Children and Young Adults in 1978 for his complete works. He now lives in Xanten in the Lower Rhine region.