Alm-Öhi, also known as the Alm-Uncle, is the paternal grandfather of the young protagonist Heidi. He lives a secluded life in a small mountain hut high above the village of Dörfli in the Swiss Alps, accompanied only by his loyal St. Bernard dog, Josef, and his goats. The villagers regard him with a mixture of fear and suspicion, fueled by persistent rumors that he was responsible for a man's death in his youth. This reputation, along with the grief of having outlived his son Tobias (Heidi’s father), has driven him to become a bitter and isolated hermit.

In the beginning, Alm-Öhi has a gruff, stern, and deeply misanthropic personality. He resents the intrusion of his young granddaughter when her aunt Dete abandons the five-year-old at his hut, and he firmly refuses to send her to school or have any engagement with the village community. He survives through his own skills, crafting wooden utensils and bowls to trade for supplies, and tending to his goats for milk and cheese, embodying a life of complete self-sufficiency.

Despite his harsh exterior, Heidi’s cheerful and affectionate nature gradually softens his temperament. Her genuine curiosity and love break through his reclusiveness, forging a deep and loving bond between them. He transforms from a reluctant guardian into a patient and caring mentor, teaching Heidi everything about mountain life, nature, and how to care for the animals. This protectiveness becomes fiercely apparent when Dete later tries to take Heidi away to Frankfurt; he vehemently opposes the plan, though he is ultimately deceived and left behind, deeply shaken by her absence.

Alm-Öhi’s role in the story is central to Heidi’s well-being and happiness. Upon Heidi’s return from Frankfurt, where she suffered from severe homesickness, he undergoes a significant personal transformation. Recognizing that she has learned to read and needs an education, he makes the monumental decision to leave the mountain. He restores a rundown house in the village of Dörfli so Heidi can attend school during the winter, a move that marks his reintegration into the community he had long rejected.

His relationships with others evolve as well. He develops a genuine mentorship with the goat herder Peter, moving from light-hearted teasing to teaching him carpentry skills, which helps Peter build a sled and win a local race. When Clara Sesemann comes to visit the Alps, Alm-Öhi plays a key role in her recovery, showing unexpected gentleness and patience. He devises physical therapy exercises using the mountain terrain and encourages her to walk, earning the trust of Clara’s grandmother, who entrusts the girl entirely to his care.

Alm-Öhi possesses notable practical abilities. He is highly skilled in woodworking and carpentry, which provides for his material needs. His extensive knowledge of the alpine environment and animal husbandry allows him to live self-sufficiently, and this wisdom proves essential for Clara’s physical rehabilitation. By the end of the story, he has completed a journey from a feared, lonely outcast to a respected and active member of the Dörfli community, demonstrating the redemptive power of love and connection.