The character Pere, known as Grand Père in French-language versions and as Alm-Onji, or the Old Man of the Alps, in the original Japanese version, is the paternal grandfather of the young heroine Heidi. He lives alone in a modest mountain hut in the Swiss Alps, above the village of Dörfli, with only his dog for company. His past is marked by tragedy: his son Tobias, a carpenter, was killed when a falling beam struck him at work, and his daughter-in-law Adelaide died soon afterward from grief and fragile health. Overwhelmed by these losses, he withdrew from village life and became a solitary figure, and the villagers came to fear him, partly because of unverified rumors that he had killed a man in his youth.

In personality, Pere initially appears stern, gruff, and distrustful, keeping visitors at a distance and showing little patience for the customs of village society, including formal schooling. This outward harshness conceals deep grief and a guarded, caring nature. He is highly self-sufficient, practical, and physically capable, able to provide for himself in the demanding mountain environment. His stubbornness is a defining trait, but beneath it lies a strong sense of responsibility and a capacity for deep attachment once his trust is earned.

His motivations shift over the course of the story. At first he seeks isolation, driven by sorrow and a desire to be left alone. When his niece Dete brings the orphaned Heidi to live with him and forces the responsibility on him, he accepts her reluctantly. As Heidi's warmth gradually reaches him, his motivation becomes love and protection for his granddaughter. He works to give her a secure home and, in time, to ensure her future well-being, even when this means overcoming his own resistance to the village and its institutions.

Within the story, Pere serves as Heidi's guardian and the emotional anchor of her life in the mountains. His initial coldness and suspicion create the early conflict, while his growing devotion provides the stability that allows Heidi to thrive. His relationship with Heidi is the most important in the series: her cheerful spirit softens his bitterness, and he becomes a devoted and fiercely protective grandfather. His connection with Dete is strained, since she leaves Heidi on his doorstep and later takes her away to Frankfurt against his wishes. With Peter, the young goatherd, he has an amiable but distant acquaintance, and his tolerance of Peter's friendship with Heidi shows his growing openness. His relationship with the villagers also evolves from estrangement to acceptance.

Pere undergoes a clear development across the series. Under Heidi's influence, he begins to reintegrate into the community: he repairs an old house in the village so that Heidi can attend school during the winter, gradually befriends the townspeople, and becomes a more sociable and contented man. His transformation is also visible in his willingness to help others, as when he takes part in the efforts to help Clara, Heidi's friend from Frankfurt, regain the use of her legs during her stay in the Alps.

In terms of abilities, Pere is a skilled and resourceful man of the mountains. He is a capable carpenter and craftsman, able to build, repair, and maintain his home and its furnishings, and he possesses the practical knowledge needed to survive the harsh Alpine seasons, including caring for the goats. His physical strength and endurance, together with his firm and patient guidance, also prove essential when he helps Clara work toward walking again. These qualities reflect a man who, despite his years of isolation, remains dependable, capable, and quietly resilient.