Moominpappa began life as an orphan in a strict Hemulen-run orphanage, where he felt misunderstood and confined. He escaped by falling through an ice hole while admiring his reflection, setting him adrift on a solitary path with dreams of exploration. During his youth, he traveled extensively, encountering pivotal figures: the inventor Hodgkins, the carefree Joxter (Snufkin's father), and the anxious Muddler (Sniff's father). Together they built the riverboat Oshun Oxtra, launching it with Edward the Booble to journey to the sea. Their daring escapades included rescuing a Hemulen's aunt from the Groke, meeting the Mymble's family on an island, and attending a royal birthday celebration. Moominpappa ultimately rescued shipwrecked Moominmamma, whom he married, establishing their family life in Moominvalley.

Characterized by a restless spirit and longing for adventure, Moominpappa frequently revisits his past exploits through memoir writing. Though yearning for novelty, he remains committed as Moominmamma's husband and Moomintroll's father, striving for responsibility and protectiveness. He perceives himself as a profound thinker, gifted storyteller, and capable problem-solver – self-assessments his family gently indulges. His restlessness periodically resurfaces, manifesting in desires like joining the wandering Hattifatteners or relocating the family to a desolate lighthouse island in search of purpose. This move, driven by dissatisfaction with domesticity, strained the family as they adapted to the barren environment, faced challenges like a reclusive fisherman, and witnessed Moominmamma's homesickness.

Physically resembling other Moomin trolls, he is white and round with a large snout, bipedal, and possesses a thin, tufted tail. His signature black top hat, inscribed inside "M.P. from your M.M." as Moominmamma's gift, distinguishes him. He often carries a black cane primarily for aesthetic effect. Some adaptations depict him with a slight bluish tint.

His relationships reveal complexity. He bonds with characters he deems intellectual, such as Hodgkins and the philosophical Muskrat. Though occasionally overbearing in offering guidance or solutions, his underlying motivation is a sincere commitment to his family's well-being. Resourceful in crises, he demonstrates practicality, exemplified by building the original Moominhouse himself. His later years reflect a gradual reconciliation between adventurous impulses and domestic stability, culminating in the family's return to Moominvalley after the lighthouse interlude.