Robert Kenneth Ressler was an American FBI agent and author. He played a significant role in the psychological profiling of violent offenders in the 1970s and is often credited with coining the term "serial killer", though the term is a direct translation of the German term Serienmorder coined in 1930 by Berlin investigator Ernst Gennat. After retiring from the FBI, he authored a number of books on serial murders, and often gave lectures on criminology.