Calcifer is a fire demon from the novel "Howl's Moving Castle" by Diana Wynne Jones. He is a small, animated flame that powers the moving castle owned by the wizard Howl. Calcifer has a distinct personality, often displaying sarcasm and a sense of humor, which adds charm to his character. In the story, Calcifer is bound by a contract to Howl, which limits his freedom. He plays a crucial role in the plot, assisting the main character, Sophie, as she navigates her adventures. Calcifer's unique abilities and fiery nature make him an essential part of the magical world.