Hazel Grace Lancaster is the main character in the novel "The Fault in Our Stars" by John Green. She is a sixteen-year-old girl living with cancer, specifically thyroid cancer that has spread to her lungs. Hazel is intelligent, introspective, and often uses humor to cope with her illness. She attends a support group for cancer patients, where she meets other young people facing similar challenges. Throughout the story, Hazel develops a close relationship with Augustus Waters, another cancer patient. Their bond explores themes of love, mortality, and the impact of illness on young lives. Hazel's journey highlights her struggles and resilience as she navigates her condition and the complexities of life and relationships.