The novel’s narrator and 16-year-old protagonist. An astute and remarkably conscientious girl, Hazel was diagnosed at age thirteen with a terminal form of thyroid cancer that has since spread to her lungs. She keeps most people at a distance, knowing her death will ultimately hurt them, until she falls in love with Augustus.
The sixteen-year-old with osteosarcoma who becomes Hazel's boyfriend. Augustus has a keen wit and a tendency toward performance—he revels in grand romantic gestures. Augustus almost immediately falls in love with Hazel after meeting her at Support Group.
The mutual friend of Hazel's and Augustus's who facilitates their introduction at Support Group. Isaac is cynical by nature. Blinded by cancer and kicked to the curb by his girlfriend Monica, Isaac often embodies skepticism and rage. It is worth noting that he shares his name with Biblical Isaac, who also was blind.
Hazel’s mother. She is an emotionally strong and kind woman who has made it her life to care for Hazel. During the novel Hazel obsesses over the emotional devastation that her death will cause to her mother. In the end Hazel is overjoyed to learn that her mother has secretly been taking classes to become a social worker.
Hazel’s father. He is caring and prone to tears. In contrast with Hazel's mother, he only understands Hazel's cancer broadly and spends much of his time at work.
The infamous author of An Imperial Affliction. Hazel and Augustus learn he is a verbose and brash drunkard who pretentiously deflects emotion with walls of intellectualism and cruelty.
The leader and sole adult at Support Group. He is noted for his warmth and unequivocal optimism. As a consequence of cancer Patrick lost both of his testicles, which provides some of the more cynical group members with a bit of comic relief.
The few glimpses that we get of Augustus’s parents in the novel are of kind and understanding people. They do not hesitate to vegetarianize Hazel’s meal. Near the end of the novel, it means a lot to Hazel when Augustus’s father whispers in her ear about how great it is that she has been involved in his son’s life.
Hazel’s primary cancer doctor. She is a strong, assertive, yet empathetic physician. At one point Hazel remarks that Dr. Maria is very into giving out hugs. She convinces Hazel’s parents that Hazel should be allowed to travel to Amsterdam, despite their reservations.
Peter Van Houten’s assistant. Initially responsible for relaying Hazel and Augustus’s communications to the author, Lidewij comes to act as a voice of reason for Van Houten.
Hazel’s friend and former schoolmate. She is pretty, popular, and exemplifies what Hazel might have been like if she hadn't been diagnosed with cancer and left school. Though they are still friends, there is a palpable distance between the two girls, who occupy such divergent worlds.
Isaac’s girlfriend and then ex-girlfriend. Monica breaks up with Isaac prior to his surgery to remove his remaining eye.
Augustus’s former girlfriend who died from brain cancer. Although we never meet her directly, we learn that the cancer changed her personality. She became selfish, impulsive, and cruel, especially in regard to Augustus. Caroline represents the realistic horrors associated with terminal cancer.
The protagonist of An Imperial Affliction. Anna is a girl of about Hazel’s age who also suffers from a terminal illness. Hazel greatly admires the honesty with which Anna deals with her cancer. An Imperial Affliction ends midsentence, causing Hazel to speculate about her beloved Anna’s fate.