Ethan is a sixth-grade boy with dark curly hair and freckles. He faces high expectations from his peers, who assume he shares his famous father's artistic abilities. Rather than admit he struggles with drawing, he produces stick figures and tries to hide his lack of talent. At home, he steps into an adult caregiving role, managing household duties and looking after his younger sister while his father experiences severe depression.

Inkling is a sentient ink splotch who emerges from Peter Rylance's sketchbook. Sustaining himself by absorbing ink from printed materials, he learns to communicate by mimicking the writing styles of the books he consumes. He possesses a strong desire to please and sets out to assist the Rylance family with their various artistic and emotional challenges.

Peter is a renowned comic book artist best known for his best-selling superhero series, Kren. For two years following the death of his wife, he has suffered from a profound block that prevents him from drawing or writing. His prolonged sadness makes it difficult for him to manage daily tasks, causing his son to manage the household in his place.

Vika is a sixth-grade student and the daughter of Peter Rylance's publisher. Widely recognized as the best artist in her class, she harbors a deep jealousy toward Ethan and frequently insults his lack of drawing skills. She actively protects her family's financial interests and views the Rylance family's artistic output as crucial to her own stability.

Karl is the mustachioed founder and owner of Prometheus Comix, the company responsible for publishing Peter Rylance's work. Facing declining sales, he urgently pressures Peter to produce new, profitable comic books. He maintains a friendly facade with his star artist but prioritizes financial gain over creative integrity.

Blotter is a large, aggressive ink entity that emerges as a counterpart to Inkling. Nourished entirely on a diet of violent, low-quality comic books, he develops a volatile personality and a crude communication style. He produces mass quantities of gruesome artwork at an alarming speed, serving as an ideal but destructive tool for a greedy publisher.

Sarah is Ethan's nine-year-old sister who has Down syndrome. She speaks about herself in the third person, treating her daily experiences as a story in which she plays the central character. She finds comfort in rigid routines, like playing veterinarian with her stuffed animals, and relies on her father and brother for support.

Soren is a light-haired sixth grader who wears glasses and serves as Ethan's closest ally. After consuming too many horror movies supplied by his older brother, he walks around with a perpetually startled expression. He offers his friends unquestioning loyalty and readily accepts Ethan's lack of drawing ability without judgment.

Olivia is Peter's deceased wife and the mother of Ethan and Sarah. Her passing two years prior to the events of the novel left a massive void in the Rylance home. Her memory continues to influence the daily lives and emotional states of her surviving family members.

Rickman is the Rylance family's pet cat. He prowls the house looking for food and serves as an early witness to the strange occurrences in Peter's studio. He acts with typical feline aggression toward the shape-shifting ink entities that move through the home.

Celine is Vika's mother and Karl's wife. She works as a teacher and spends her time at home grading papers. She acts warmly toward Ethan, having been a supportive presence for the Rylance family after Olivia's passing.

Heather Lee is a student in Ethan's sixth-grade class. Ethan has a crush on her, which makes him eager to interact with her. She uses these interactions to pass fan mail to his famous father, as she is a devoted follower of the Kren comic series.

Pino is a sixth-grade student in Ethan's class. He collaborates with Ethan, Soren, and Brady on a school graphic novel assignment, fully expecting Ethan to deliver brilliant illustrations for their project.

Brady is a classmate of Ethan and Soren. He works alongside them to construct a graphic novel for school, sharing the group's assumption that Ethan possesses natural artistic talent because of his famous father.

Mr. Sawyer is the art teacher at Ethan's school. He experiences utter bewilderment when he unlocks his classroom to find highly sophisticated ink drawings replacing his students' basic art projects.