A serial killer is an individual who commits a series of two or more murders, typically with a psychological motive. These crimes are often characterized by a distinct pattern or method, and the killer usually has a specific profile or target. The motivations can vary, including psychological gratification, financial gain, or revenge. The term is often associated with notorious figures in criminal history, such as Ted Bundy or John Wayne Gacy. Law enforcement agencies study these cases to understand the behaviors and patterns of serial killers, which can help in preventing future crimes and capturing offenders.