According to the third novel Library of Souls, Jack 'Caul' Bentham is siblings with Miss Peregrine and Myron Bentham. Born male, he did not inherit the time controlling ability Miss Peregrine has. Jealous of his sister's power and privileges, Caul would bully his infant sister just for the fun of it and grew up to hate and despise her and ymbrynes in general. As he grew, he became obsessed with the legends of Abaton and the Library of Souls which supposedly houses the souls and abilities of deceased peculiars. Rallying misguided and dissatisfied peculiar youths, most of whom are male, he started a political movement meant to overthrow the ymbrynes as the rightful leaders of peculiardom, promising to lead the peculiars to enslave humanity and rule the world like how it was eons ago when peculiar giants were the dominant creatures. In reality, however, Caul only wanted to install himself as the leader of peculiardom and reshape the world in his image, with his followers being nothing more than cannon fodder and his brother Myron imprisoned when the latter started to question his motives. When Myron realised how dangerous Caul had become, he purposely spread rumors on how to manipulate loops into granting permanent longevity when it was, in fact, an 'arcane and largely forgotten procedure to collapse loops, quickly and permanently, in an emergency'. Falling for the trap, Caul and his followers performed the infamous and controversial experiment in a Siberia loop, which ended devastatingly and turned them into hollowgasts. At some time before the setting of Miss Peregrine's Home for Peculiar Children, Caul managed to feed on enough peculiars and evolved into a wight. He began leading his former followers once more to destroy the ymbrynes and gain access to the Library of Souls, this time with guns to replace the powers his wights had lost. He sent the wight Golan and the latter's hollowgast Malthus to eliminate the famed Hollowgast-slayer Abraham Portman and kidnap Miss Peregrine and Miss Avocet, thus laying the setting for the first novel.
Miss Peregrine's Home for Peculiar Children Edit
Caul first appears in his bird form nearing the end of the first novel, stuck in a floating birdcage in the sea. He was released there by the Wights in a U-boat after they managed to capture Miss Avocet and the real Miss Peregrine in order to keep tabs on the peculiar children. He was soon 'rescued' by Emma and tagged along with the children in her canoe away from Cairnholm under the identity of Miss Peregrine.
Hollow City Edit
Still spying on the unaware peculiar children, Caul remained in his peregrine form through the journey to Miss Wren's London loop while faking his inability to transform back into 'human' form. In this installment, Caul plays the passive role of monitoring the children's progress without directly aiding or sabotaging their escape from the wights. Uncharacteristically of Ms Peregrine, he killed Winnifred the pigeon in the St. Paul's Cathedral loop, and it is unknown if he wanted to fake Miss Peregrine losing her humanity, silence the pigeon before its nervous behavior roused suspicion or just wanted to kill it. His identity is revealed at the end of the novel when he transformed back into a wight in Miss Wren's hideout of his own will, revealing to the peculiars and ymbryne that he had been stalking them all the while, even capturing the Menagerie and placing the ice fort under siege with his wights. He then initiated a scuffle and tried to take Althea as a hostage, only to stab her with an icicle when she tried to freeze him. With her dead, the ice began to melt away, allowing Caul's wights to storm the fort, capturing all the peculiars and Miss Wren. He then brought his captives to modern day London before escorting them back to his hideout, the Devil's Acre, thus ending the second novel.
Library of Souls Edit
Having brought his captives to the Devil's Acre, he managed to threaten the ymbrynes to unlock the door to Abaton, only to realize he needed a special peculiar, a Librarian, to see and manipulate soul jars to grant Caul its abilities. Anticipating Jacob and Emma's plans to rescue the rest of the peculiars and ymbrynes, Caul set a trap to injure, if not incapacitate them with a swarm of hollowgasts, only for Jacob to control all of them to turn the tide against the wights. Apparently defeated, Caul managed to escape and convince an exasperated Myron to capture Miss Peregrine with his grimbear, taking advantage of an ash storm. Taking Miss Peregrine hostage, Caul entered the Library of Souls where soul jars of ancient peculiars are stored. After having Jacob to empty a soul jar into the spirit pool, Caul shot him in the chest so no one else, especially his brother, could gain power from other soul jars, leaving him as the only peculiar giant alive. Unknown to him, Myron ingested the peculiar soul of Abraham Portman, also a Librarian, and absorbed the soul of another great ancient peculiar while Caul was busy trying to have his revenge against his sister, Miss Peregrine. In the ensuing battle between Caul and Myron, the ymbrynes attempted to collapse the Abaton loop while Caul was distracted, resulting in the loop closing with Caul (and Myron) still stuck inside, leaving him presumably trapped forever, if not dead.
Nearing the end of Hollow City, Caul is described as 'a stunted little man with knobby knees and a balding head and a nose like a used pencil eraser' right after his transformation from a peregrine into a wight.
Like other wights, Caul looks like an ordinary human with pure white eyes. However, he has a 'weird pair of knobby protrusions' near his shoulder blades, a telltale sign that he can shape-shift into a bird. Otherwise, he does not appear to be much different from any other wight. In his peregrine form, he looks exactly like Miss Peregrine in bird form, complete with black peregrine eyes.
In a picture in chapter four of Library of Souls, Caul was shown to have hair before he turned into a wight, while he was described to be balding in Hollow City (as mentioned above). This could mean that while wights and hollowgasts are essentially immortal, they could still lose their hair naturally, especially when they were balding when the Experiment took place. Note that the picture of Caul and Myron was taken before their relationship soured, perhaps years or even decades before the Experiment took place. By then Caul's physical condition may have worsened by then, enough for him to start balding.
Caul is described by his brother as smiling only when he is trying to get something out of someone.
Although a wight, Caul does have a peculiarity: shape-shifting. Being the brother of Miss Peregrine, he shares the same ability to turn into a peregrine without the aid of ambrosia or external spells. Due to his gender, however, he is not a true ymbryne and cannot manipulate time to maintain loops. However, his shape-shifting peculiarity proves useful in allowing him to deceive the peculiar children into thinking he was Miss Peregrine, thus gaining knowledge of the whereabouts of the Menagerie and Miss Wren's loop in London.
It is known that Jack "Caul" Bentham has the siblings Myron Bentham and Alma LeFay Peregrine. It is very likely that Caul is the eldest among them; he is old enough to abuse his sister when she was an infant and Myron was mentioned to be 'Miss Peregrine's younger, weaker brother' in Hollow City during his merging with an ancient peculiar soul. In the first book it is made out that he is younger than Alma. Alma shows Jacob a photo of herself and says she was the youngest ymbryne, Jacob points out that two boys look younger than she does and Alma says that they are her younger brothers and that all ymbryne's are female. By the last book though it is mentioned that he is older as he tormented her when she was a baby.
- In his peregrine falcon form, Caul is the only wight to have eyes with black pupils.
- He is also the only wight to retain his peculiarity. This might be due to bird shape-shifting being a special ability, capable of resisting the effects of the experiment.
- Despite the experiment, Caul is able to regain his memory after being turned into a wight, reinstating himself as the leader of the wights like before.
- It is unclear how Caul managed to update his wights on the peculiar children's journey during the events of Hollow City while staying in his bird form.