Diabolique is an enigmatic, seemingly six year old girl who continually seeks out surrogate parents, which she typically slays before moving onto another set. She eventually "adopted" Randolph DeGuzman, a former sect leader of the Darkholders (a cult worshiping the demon Chthon through his book, the Darkhold), and an unidentified demoness. Soon after, DeGuzman began to pursue his goal of reassembling the scattered pages of the Darkhold, and killing Victoria Montesi, whose ancestors had guarded the pages. DeGuzman was actively pursuing his goals when Diabolique and her mother returned to his life. Diabolique made a room for herself in the Interpol headquarters, which DeGuzman used as his Darkholder base. She pretended to be the loving daughter, even as she was secretly assembling members of her father's own Darkholder Cult as her unwilling but helpless servants in her pet familiar, Playmate. Realizing that most of his Darkholder's were mysteriously missing, Diabolique’s father became suspicious and eventually caught Diabolique in the act of killing her adoptive mother. To placate him she promised to give DeGuzman a glimpse of Chthon, knowing full well that even a momentary view of the demon's true form would drive her mad.
Diabolique then decided she needed new parents. Her deceptively childlike appearance fooled civilians Blanche and Merle Haverford and they brought the poor child into their home by the end of the week, both Haverford's were dead. Diabolique then summoned the demon prophet, Whisperer, also known as the Voice of Chthon and offered the Haverfords to Whisperer if he granted Diabolique answers to any three questions. The Three questions gave Diabolique important information on the past history and true nature of Victoria Montesi. Diabolique then led the Darkhold Redeemer Louise Hastings to Victoria's files in the Vatican and pulled a file, which revealed Victoria's past to Louise.
Diabolique surfaced again in New York and returned to her pattern of adopting and destroying new parents. This eventually brought her into conflict with the NYPD officer Michael Badilino and his secret identity, Vengeance. By the time Diabolique escaped from Vengeance she had lost her Playmate, her spider Zoroaster and was embarrassed in front of Dr. Strange's foe, the sorceress Salomé.
A short time later, Diabolique ended up in a children’s hospital, powerless because she was unable to create a new Playmate to enhance her power. There she met and befriended Paranormal Law Enforcement officer, Rebecca Taylor. Mike Clemson, of the government agency the Conclave, and Reverend Nice eventually freed Diabolique, wanting her to help them destroy Vengeance. To help Diabolique regain her powers Reverend Nice offered his own wife, Wendy Sue, to Diabolique as raw material for the construction of a new Playmate Familiar. Diabolique used her renewed power to confront Vengeance/Badilino and killed the hero’s girlfriend Rebecca with sympathetic magic. Diabolique then framed Badilino for Rebecca’s death and teleported to parts unknown.