Robert Ressler was an American criminal profiler and former FBI agent, known for his pioneering work in the field of criminal psychology. He played a significant role in developing techniques for understanding and capturing serial killers, contributing to the establishment of the FBI's Behavioral Science Unit. His insights helped law enforcement agencies better understand the motivations and behaviors of violent offenders. Ressler is also credited with coining the term “serial killer” and was involved in interviewing notorious criminals, including Ted Bundy and John Wayne Gacy. His work has influenced both law enforcement practices and popular culture, including books and films about criminal profiling.