Diabolique is an enigmatic, seemingly 6-year-old girl, who continually sought out surrogate parents, which she slew before moving to another set.

Diabolique became the daughter of DeGuzman, the former head of a sect of the Darkholders (a cult worshipping the demon Chthon, through his book, the Darkhold), and an unidentified demoness. When she first made her presence known, she was already feared by the Darkholders, indicating she had long been a threat to them.

In recent years, DeGuzman sought to reassemble the pages of the Darkhold, and to slay Victoria Montesi, last in the line of the family that had opposed the Darkhold throughout the ages. It was at that point that Diabolique and her mother returned to her father's life. She made a room for herself in the FBI building which DeGuzman used as his Darkholder base. She pretended to be the loving daughter, while she slowly encountered and slew several Darkholders, creating a new Playmate, and enhancing her power. As DeGuzman continued his plans against Montesi and her allies, Diabolique methodically wiped out most of the Darkholders. DeGuzman investigated, in time to see Diabolique slay her own mother, and then playing with her eyes. She promised to give DeGuzman a glimpse of Chthon, knowing full well that to actually glimpse the true form of the demon would drive him mad.

With the Darkholders slaughtered, her mother dead, and her father a drooling lunatic, Diabolique decided that she needed new parents. She wandered to the home of Blanche and Merle Haverford and spent a week with them. How she spent that time is not known, but by the end of the week, both of them were dead. She then summoned the demon prophet, the Whisperer, also known as the Voice of Chthon. The Whisperer granted her answers to any three questions in exchange for her two victims as sacrifices. The three questions all gave Diabolique information on the past history and true nature of Victoria Montesi.

Diabolique then invaded the Vatican and confronted Montesi's friend and fellow Darkhold Redeemer, Louise Hastings, leading her to Victoria's fathers files. Diabolique had pulled one specific file, which revealed Victoria's past to Louise.

Diabolique was next seen after she had taken control of a another human couple, making them her victims and forcing them to be her parents. She proceeded to kill several people in the subways, enabling her Playmate to grow further in power. The couple eventually gained sufficient strength to resist her and jumped in front of a subway, killing themselves. Diabolique, believed to be an innocent and traumatized orphan, was brought to social services, where she encountered Lt. Michael Badalino, who was investigating the subway deaths. Wanting Badalino to be her father, Diabolique followed him to the subway where he encountered the Playmate, in the process of slaughtering another victim.

Recognizing the threat of the Playmate, Badalino transformed into Vengeance and attacked it. Feeling that Badalino had deceived her by pretending to be human, Diabolique sent her spider, Zoroaster to attack Vengeance as well. However, Diabolique then sensed the power of the demon sorceress, Salomé whom she wished to be her mother and mentor. She withdrew her Playmate and confronted Salomé expressing her desires. Vengeance managed to overpower and destroy Zoroaster, and then tracked Diabolique and again confronted her. Intrigued by the power of the young witch-girl, Salomé agreed as long as Diabolique could pass her test: destroying Vengeance.

Diabolique badly injured Vengeance by attacking him with her voodoo doll, but Vengeance managed to destroy Playmate with a blast of hellfire, rendering her powerless. Salomé teleported Vengeance away, allowing Diabolique to escape. Salomé agreed on the potential for a future apprenticeship after Diabolique created a new Playmate. Within days, Diabolique was on the hunt for a new mother.

A short time later, Diabolique ended up in a children's hospital, powerless, where she was unable to create a new Playmate for power. While there, she met and befriended Rebecca Taylor, a member of the Paranormal Law Enforcement Team. Diabolique was freed by Mike Clemson, of the government agency, the Conclave, who sought to destroy Vengeance. Clemson's ally, Reverend Nice, also eager to destroy Vengeance, offered his own wife, Wendy Sue, to become her new Playmate. Diabolique then confronted Vengeance, and used her sympathetic magic to kill Rebecca, who was also the girlfriend of Badalino, and frame him for her death. She teleported away before he could stop her.