Caroline Mathers is Augustus’s ex-girlfriend, and although she never appears in the novel directly, her character serves as a representation of cancer’s domineering effect and significantly impacts the way Hazel and Augustus navigate their relationship. In Chapter 5, Augustus explains to Hazel that his ex-girlfriend passed away less than a year ago, and she discovers that Caroline suffered from a personality-altering brain cancer in Chapter 6. These changes, which led her to act aggressively and frequently berate Augustus, challenge the stereotypical representation of children with cancer as brave and heroic. Caroline’s cruel behavior is almost a physical representation of the brutal nature of cancer itself and works to create a juxtaposition with Hazel’s character, one which emphasizes the notion that cancer does not follow a single narrative.
The way in which Caroline’s particular cancer story unfolded influences both Hazel and Augustus in the early stages of their relationship, adding an element of fear and hesitation that complicates how they feel about one another. When he first sees Hazel at the Support Group, Augustus is taken aback by how similar she looks to what Caroline looked like leading up to her death, and this association initially makes him skeptical of her. Even when he manages to look past appearances and opens himself up to Hazel, she continues to struggle with the idea of establishing a relationship doomed to end in heartbreak. Hearing Caroline’s story and seeing her family’s posts online drives Hazel to explicitly tell Augustus that she cannot become romantically involved with him, a reaction which reflects her fear of becoming a “grenade” to those around her. While she eventually overcomes this anxiety, Caroline’s character adds to the inner turmoil that she feels as she navigates a new stage of her life.