Hazel is the narrator and protagonist of the novel, a 16-year-old girl with thyroid cancer that has spread to her lungs. Cancer very nearly killed her at age 13, and though an experimental drug has stopped the growth of her tumors for the time being, she is not expected to live long. Hazel is highly intelligent. Living under the constant threat of death has made her both more mature and more cynical than most of her peers. Until she meets Augustus, her life is bookish and withdrawn; too ill to attend high school, she takes a few community college classes and spends her days reading classic literature and watching trash TV. Her main fears about cancer and her own mortality are not for herself, and the experiences she will miss out on, but for her parents and how they will cope after she is gone. This attitude is a hallmark of her caring, unselfish nature.

Augustus is the novel’s other main character, a 17-year-old former basketball star who has lost his lower leg to bone cancer. Augustus has a native optimism and a humorous, carefree outlook that counterbalances Hazel’s more guarded pessimism. He loves video games, adventure novels, and action movies, and maintains a more active social life than Hazel.