Jacob is described as skinny.
It was revealed in the end of Chapter 8 and the beginning of Chapter 9 in the first book that, like his grandfather, Jacob has the ability to see hollows unlike other peculiar children who could only see their shadows. This explains why Ricky Pickering wasn't able to see the dark shadow Jacob was describing the night his grandfather was killed. It was also revealed that in the ending of Hollow City, Jacob was able to talk to and control hollows and starts to develop it in the Library of Souls. He also has the ability to see the soul jars because his peculiar ability is originally to be a librarian in the library of souls.
Abraham Portman plays an important role in Jacob's childhood. Jacob looks up to his grandfather, owing to the fact that he tells fascinating stories about his own life. This includes stories of the hollowgast and peculiar children residing in Miss Peregrine's Home For Peculiar Children.
Miss Peregrine's Home for Peculiar Children
In the book Miss Peregrine's Home for Peculiar Children, Jacob Portman is first seen as a young child. Jacob discusses how his grandfather showed him photos of the peculiar children, Jacob then grows up believing these tales were false and a figure of his grandfather's imagination. Jacob then one day receives a distress call from his grandfather and rushes to find him but only to find him slain at the hands of a mysterious beast. In his grandfather's dying words told him what he thought to be a riddle, but was actually straightforward instructions. The "riddle" was about passing the old man's grave and going into the time loop, and Jacob just believes this is more of his grandfather's ramblings. Jacob then catches a glance of the creature that murdered his grandfather only to find that others could not see it. Dr. Golan, Jacob's psychiatrist, suggests that he takes a visit to Wales. Jacob is accompanied by his father to Wales where he find an old suitcase filled with more pictures of the peculiar children. During one of his adventures Jacob visits his grandfather's old orphanage where he encounters Emma Bloom, his grandfather's old love interest and a peculiar with the ability to manipulate fire. Jacob then stumbles across a bar, where the people accuse him of being a Nazi and at this point Jacob had unknowingly entered the loop his grandfather told him about. Emma and an invisible boy named Millard Nullings rescue Jacob and take him to Miss Peregrine, as Emma believes him to be a wight. Miss Peregrine then informs Jacob about his grandfather's past with the peculiar children, and Jacob is introduced to the other peculiar children that his grandfather had showed him pictures of.
In the beginning of the Hollow City, Jacob Portman doubted himself to be able to keep all of the children safe for he doesn't know how to completely use his peculiarity. As the story progresses, his peculiarity develops the more he uses it. While he was deciding whether to leave the children and go back to his normal life or not, he was sleep walking where at the end of his dream, Abraham reveals to him "Don't fight the pain, that's the key.. It's telling you something. Welcome it, let it speak to you. The pain says: Hello, I am not other than you; I am of the hollow, but I am you also.". At the end of the sequel, when Jacob was about to be eaten by the hollow that followed him, Emma and Addison escaped from the wights. He thought to himself that we was as good as dead and he couldn't do anything else but to just stop fighting. Then a strange thing happened, the pain shifted and became something else. He has discovered something quiet and gentle. That is when Jacob realized that he could control the hollows as long as he stays calm and concentrated.
Library of Souls
Abraham is Jacob's grandfather. Immigrating from Poland to Wales and then, finally, to America. Due to his knowledge of peculiars, he is initially discredited as being senile. It was he who told Jacob stories of the children's home, and was very insistent that Jacob believe him, as he was aware of Jacob's peculiarity, he himself sharing the talent. His stories led to Jacob's eventual discovery of the home. Unfortunately, he is deceased from death by Mr. Barron.
Maryann Portman is Jacob's rich, socialite mother. Demonstrating extreme vanity, it is often mentioned that she enjoys showing off her wealth. Although well meaning, she and her son have a rocky relationship, she beliefs that her son has gone quite mad, and he resenting her blatant disaffection for him.
Franklin is Abraham's son and father to Jacob. He and his son clearly demonstrate a somewhat closer relationship than Jacob and his mother, both understanding one another to some degree. It is he who accompanies Jacob to Wales in the first novel but then thinks that they shouldn't have gone to Wales
He is Jacob's best and only friend before the peculiar children came along. He is a screw up and a rebel but Jacob is friends with him because he needs him as a bodyguard, but Ricky uses Jacob as a person to help him pass. He was with Jacob when he found Abraham Portman dead in the woods.
Bronwyn is a friend of all at the home, including Jacob. She accompanied him, along with Emma and Millard on the expedition to locate Miss Peregrine in the first and second novel.