Known in the village as Alm-Uncle or Alm-Onji, Grandfather lives isolated in a remote Swiss Alps mountain hut with only his Saint Bernard, Josef, prior to Heidi's arrival. Villagers widely perceive him as a bitter, reclusive, and misanthropic figure, feared and avoided due to his gruff exterior and aloof nature. This isolation stems from a past entangled in village rumors and misunderstandings, fueling his initial reluctance to accept his orphaned granddaughter, Heidi, whom he only takes in under pressure from her aunt, Dete.

Heidi's presence transforms his existence. Her innate kindness, boundless enthusiasm for mountain life, and unconditional affection gradually wear away his emotional barriers. Witnessing her joy in simple pleasures – tending goats, exploring pastures with the young goatherd Peter, caring for animals – softens his demeanor. He evolves from a reluctant guardian to a deeply devoted caregiver, teaching Heidi traditional skills like cheese-making and nurturing her bond with the natural world. This shift reveals his underlying capacity for profound love and protectiveness, shown through quiet acts like ensuring her comfort in harsh winters and building her a proper bed.

The forced separation when Dete takes Heidi to Frankfurt as a companion for the invalid Clara Sesemann exposes the depth of his attachment. He becomes visibly shaken and emotionally devastated, sitting in silent despair. His vulnerability surfaces when Peter confronts him, enraged by Heidi's departure; instead of sternness, Grandfather trembles and admits he never expected Heidi to leave, revealing the extent of his emotional wound.

Heidi's return due to severe homesickness restores their bond. Grandfather actively supports her readjustment, including encouraging her schooling. When Clara visits the Alps, his nurturing extends to her. He participates in her physical therapy alongside Heidi and Peter, patiently helping her strengthen her legs over months. This culminates in Clara gradually gaining the ability to walk and then run, reflecting Grandfather's supportive role in her recovery within the cherished natural environment. His core identity remains rooted in the solitude and rhythms of the Alpine landscape, but his journey marks a significant internal shift from isolated bitterness to a quietly expressed, deeply felt capacity for familial love and care.