"Family annihilator" is a term used to refer to someone who commits familicide, the act of killing one's own family, usually immediate members, but instances of the perpetrator targeting other relatives, such as in-laws, are not unheard of. Reasons for familicide vary, and can include:
- Spite or revenge (for example, a former spouse killing their ex-partner and the children due to custody issues)
- A twisted act of mercy
- Mental illness or instability, such as severe depression caused by multiple real or imagined failures
Out of all forms of mass murder, familicide is regarded as the most common, and often ends with the perpetrator (who is almost always male) committing suicide.
- John Vincent Bell ("The Fight"): Murdered father-daughter duos in a ritual, then killed the mothers, whom he informed of his victims' abductions, in order to eliminate any loose ends.
- William Meeks ("Here is the Fire"): A religious man who, after his wife died from giving birth to their fourth son, who also died, felt that his other three sons must die so then they could be "saved". He planted pipe bombs in public places where his sons would go to, so numerous others can also die and place him out of suspicion. He only managed to murder one son, who was among those killed in a school bombing, while the other two were rescued by the Red Cell team.
- Veronica Day ("The Time is Now"): Veronica would manipulate teenage boys into killing their parents with a shotgun. She can be considered a family annihilator in the sense that her mission is to "destroy" families.
- Ronald DeFeo, Jr.: With no discernible motive, he shot his father, mother, two brothers, and two sisters to death while they slept in their home, 112 Ocean Avenue, which later became infamous as the site of an apparent haunting dubbed "the Amityville Horror".
- Dipendra of Nepal: Nepali prince, and the perpetrator of the Nepalese royal massacre, in which he murdered nine members of his family, and wounded five others, before attempting suicide by shooting himself in the head (dying three days later after falling into a coma).
- John List: Shot his mother, wife, two sons, and daughter to death, claiming to have done so because he wanted to spare them "the shame" of having to live with a man who failed to support them in his role as patriarch (List had been recently fired, and had incurring massive debt).
- Ronald Simmons: Spree killer who began his rampage by wiping out fourteen members of his family through various means around Christmas. The victims included his wife, eight children (one of them the result of an incestuous relationship with a daughter), three grandchildren, a daughter-in-law, and a son-in-law.
- Dennis Rader, the BTK Killer: During Rader's first known murder, he killed the entire Otero family: the father, Joseph Otero, the mother, Julie, and their children, Joseph Jr. and Josephine. All of them were either strangled, suffocated or, as with the daughter, hanged. It should be noted that, when he killed Shirley Van Relford, he tied up her children and put them in a bathroom to get them out of the way, even leaving a few toys and blankets inside for them to make it as comfortable for them as possible.
- Leonard Lake and Charles Ng: In a way, Lake and Ng can be considered family annihilators as they would on occasion kill entire families, disposing of the men and children before raping, torturing and killing the women.
- Yang Xinhai, the Monster Killer: A prolific Chinese serial killer whose spree lasted from 1999 to 2003. He almost always killed entire families, breaking into their homes in the middle of the night with an assortment of makeshift weapons, such as shovels and meat cleavers.
- Anatoly Onoprienko, the Beast of Ukraine: A Ukrainian serial/spree killer who was convicted of killing 52 people, between 1989 and 1996. 43 of them were killed in the last six months of his rampage. He would target entire families or groups of people, kill everyone, including possible witnesses, with a variety of weapons, including a hunting rifle, a double-barrelled shotgun, an axe and a hammer.
- John Linley Frazier, the Killer Prophet: In 1970, he entered the home of eye surgeon Victor Ohta and killed him, his wife, children and secretary with a .22 handgun. All victims were bound and blindfolded with colorful scarves from the house. Frazier then set the house on fire and left a rambling note on Ohta's car. He claimed his motivation for the massacre was that "voices from God" had told him to "seek vengeance on those who rape the environment".