Serial Killers: Not All Serial Killers Are Insane To be sane is to be mentally sound and healthy, according to the Merriam Webster Dictionary. Insanity as defined by the Merriam Webster Dictionary as exhibiting serious and debilitating mental disorder. Serial killers are seen by most people as being insane. This is not the case. Some of the most famous serial killers were some of the smartest and clever individuals of their time. Many serial killers, though wrong in what they do, are some of the most intelligent people to have lived. Jack the Ripper is the most elusive and mysterious serial killer who has been recorde