Heidi is a young orphan girl who stands as the central figure of the story. Her background is marked by loss, as she lost her parents when she was an infant, leaving her to be raised by her Aunt Dete. Around the age of five, her aunt, unable to continue caring for her due to work obligations, brings her to live with her reclusive paternal grandfather in the Swiss Alps, a place that becomes her true home. Her given name is Adelheid, but she is known affectionately by everyone as Heidi.

In terms of personality, Heidi is defined by her remarkable cheerfulness, boundless energy, and an infectious optimism that profoundly affects those around her. She is a cheerful and intelligent child, driven by a deep curiosity and a genuine, unreserved love for all living things. She has an inherent, almost magnetic kindness that allows her to see the good in people, even when they are initially hostile or standoffish. Her primary motivation is a simple yet profound desire for freedom and connection with nature. She is happiest when running barefoot through the mountain meadows, befriending the goats, and feeling the sun and wind. This deep-seated love for her pastoral life is her greatest source of strength and also her central point of conflict when she is removed from it.

Heidi serves as the story’s catalyst for change. Her role is not that of a conventional hero who performs great deeds, but rather as a force of nature whose pure-hearted presence transforms the lives of everyone she meets. Her relationship with her grandfather, Alm-Öhi, is the most significant. Initially a bitter hermit feared by the local villagers, he slowly defrosts under Heidi's persistent, non-judgmental affection, rediscovering love and purpose through her. She also forms a close friendship with Peter, a young goatherd. Though they occasionally bicker, their bond is strong, and she brings joy to his family, particularly his blind grandmother, for whom Heidi’s presence is a rare light. Her role in the Sesemann household in Frankfurt is similarly transformative for Clara, a wealthy, lonely, and physically disabled girl. Heidi’s vibrant stories of the Alps and her sincere friendship offer Clara a happiness she had never known.

Heidi undergoes significant development, primarily through her painful journey to and from Frankfurt. Forced to live under the strict, repressive rules of the housekeeper Miss Rottenmeier, who even forbids her from mentioning the mountains, Heidi’s free spirit is crushed. The contrast between her wild, open life on the mountain and the confined, rigid city existence causes her to fall into a deep depression and become severely homesick. This distress manifests physically as she grows pale and thin, and psychologically as she begins to walk in her sleep. This crisis ultimately forces the household to send her back to the Alps. Upon her return, she can finally read to Peter’s grandmother, fulfilling a promise, and her recovery is immediate. Her resilience is showcased as she bounces back to her former self, and her experiences allow her to bridge her two worlds when Clara comes to visit the mountains.

While Heidi possesses no supernatural abilities, her notable traits are her profound empathy and her status as a friend to all living things, from the goats and birds to the family dog Joseph. She has an almost stubborn resilience and a powerful ability to endure hardship by holding onto the memory of her beloved mountains. Her physical vitality is notable; she is strong from years of outdoor living and strongly prefers to go barefoot. She also learns to read in Frankfurt, a skill motivated by her desire to help others, which she uses upon her return to the Alps to read psalms to Peter’s grandmother.