- "Is he dead? Yay! Oh.. No, he's hanging on to the shutters. Shame. Still, this is definitely the funniest thing I've ever seen. You three really are incompetence on a stick."
- -The skull reveling at Lockwood & Co.'s difficulties on a job, The Hollow Boy
The skull was the name given to a particularly pernicious male Type Three ghost, trapped within a human skull and encased in a glass jar. Liberated from the possession of the Fittes Agency by George Cubbins, the skull came into the possession of the Lockwood & Co. agency. There, it underwent torturous experiments at the hands of Cubbins before revealing itself by talking to Lucy Carlyle, a new agent for the company. The skull sometimes provided useful information to the group, but also had a habit of being perverse, revealing dangerous secrets, and nonchalantly suggesting casual murder as a solution to problems.
Little is known of the skull's past history prior to entering ghosthood. It is believed that he was for a time, prior to death, a disciple of Dr. Edmund Bickerstaff, a man obsessed with the secrets of death who created a dangerous relic known as the bone glass.He was extremly proud of being his servant, and even during his ghosthood, attemps to help him. (->The Whispering Skull, Lucy discovers that George Cubbins and Quill Kipps have been kidnapped by A. Joplin (Researcher obsessed by the ghost of Edmund Bickerstaff and his -Bone Glass-). The skull describes him as -a great man, a visionary, a pioneer that came to a sad end-.
The skull's previous human form, as seen by Lucy Carlyle while on the other side, is described as "slouching in a corner..., a thin and rangy youth, hair spiked, hands in pockets," with his distinguishing grin, "which gleamed sardonically." 
After death, this individual became a Type Three ghost. The rarest and most unusual of spirits, Type Threes had the power to communicate directly with those possessing the proper Talent. He was some point trapped within a skull placed within a sealed jar and claimed by the Fittes Agency, which claimed the relic would be disposed of in its furnaces, but which was actually planning to take it away for its own studies. The jar, however, was stolen by George Cubbins, shortly following his dismissal as an agent with the company.
With Lockwood & Co.Edit
Following its theft, the skull was trasnported to 35 Portland Row, London, England, where it became the property of the Lockwood & Co. agency, Cubbins's new employer. There, it was subjected to numerous experiments in the hope of discerning its nature. Cubbins would shift it from place to place, run the jar under water, place it in the oven, anything in the hope of provoking a reaction. The ghost, however, would only manifest as a murky green plasm which would sometimes congeal itself into the visage of a face and make rude expressions.
Things took a sudden turn following the hiring of Lucy Carlyle as an agent with Lockwood and Co. Following the first major successful case with Carlyle on the job, the skull chose to speak with her, revealing itself to be a Type Three ghost. It told her that "Death is coming", but after she informed her fellow agents of the discovery, it reverted back to its previous form and would not speak again. Though they tried a variety of experiments, it did not speak again for many months, though it would still sometimes materialize. During this period, it was again subjected to various tortures by Cubbins, including placing it in daylight during the noonday sun and baking it in an oven.
Finally, as Lockwood & Co. began investigations on a particularly challenging case, the skull broke its silence. To everyone's irritation, the skull provided little information or insights at first. It actually first insisted on speaking to Carlyle alone, insulting her intelligence, calling Cubbins "fat," and suggesting that Anthony Lockwood was deceitful, referring to a locked room in 35 Portland Row, one which it claimed Carlyle would never have left alive had she entered. Afterwards, Lockwood and Cubbins entered the scene and the skull again cut off communication, leaving the group to stew with the insinuations it had made. Following this, the skull was again subjected to a series of experiments by Cubbins in the oven, but after six minutes of 300 degrees fahrenheit heat, he was only able to get it to form rude expressions.
- "Here's my tip: lure her down to Kitchenware and brain her with a skillet. ... Holly. It's a golden opportunity. There are lots of pointy things there too, if you prefer. But basically a simple smack with a rolling pin would do fine."
- -The skull, suggesting murder a solution to Lucy's personnel problem, The Hollow Boy
The skull was perverse and sarcastic, often delighting in its attempts to foment conflict between the members of Lockwood & Co. It also possessed a violent nature, having no problems with casually suggesting murder as a solution to problems. Despite this, the skull could be helpful, and sometimes provided vital assistance that made the difference in cases for Lockwood and Co. The skull also seemed to value companionship, as its misbehavior could sometimes be quelled by Carlyle's threats to abandon it where it would never be found if it didn't help. Following Carlyle's departure from Lockwood & Co. and subsequent hiring as a freelance agent, the skull was her only regular companion in her independent investigations. It often aided her, while maintaining its sarcastic personality, and would sometimes talk with her when she was otherwise alone at home. After she agreed to again work a case with Lockwood and Co., it began for a time treating her as a "jilted lover," though things took a turn when the skull was unexpectedly stolen from her.
The skull abhorred George Cubbins, who had regularly tortured it in the past. It nevertheless sometimes seemed bemused by Cubbins and his fascination with the mysteries of the afterlife. The skull also detested Holly Munro, who was fussy and insisted on keeping it covered with a cloth. It seemed amused by Carlyle's friction with Munro and sometimes suggested methods for her murder. Though not as antagonistic towards Lockwood as Cubbins, the skull nevertheless created friction by hinting that Lockwood was keeping dark secrets from Carlyle. Despite oftentimes being antagonistic with her, the skull in some ways seemed to value the rapport it had built with Carlyle once it had begun speaking to her.