Whenever magazines and newspapers dealt with the topic of sexuality in the 1960s, 1970s and 1980s, the psychologist Helmut Kentler (19282008) was often quoted; his book "Parents Learn Sex Education", published in 1976, became a bestseller. Kentler was also present almost all the time on radio and television. Today, however, he is criticized for his advocacy of sexual contact between children or adolescents and adults. The book traces Kentler's multifaceted biography and seeks answers to various questions such as: Who or what favored him receiving a professorship at the University of Hanover in 1976? Why did Kentler demand the legalization of sexual contact between children or adolescents and adults? For what reasons was this demand relatively little criticized for a relatively long time? The book is based on numerous sources, including various archive materials and interviews with contemporary witnesses.