Moominpappa stands as a central figure in Moominvalley, married to Moominmamma and father to Moomintroll. Orphaned in his youth, he lived under a strict Hemulen headmistress at an orphanage before running away to explore the world, fostering a deep restlessness and thirst for adventure. Venturing out alone, he navigated a dark forest where he met the inventor Hodgkins, the Muddler, and the Joxter. Together, they finished building the riverboat Oshun Oxtra and embarked on journeys. They faced sea monsters and aided others, such as saving the Hemulen's aunt from the Groke, experiences that cemented Moominpappa's reputation as an explorer and storyteller.

Despite this adventurous past, Moominpappa chose to settle down, committing to family life and striving to be a responsible father. He resides with his family in Moominhouse, often engaging in deep thought and sharing his wisdom, viewing himself as a great thinker and storyteller. His family indulges these traits, with Moominmamma particularly supportive of his heroic self-image. He documents his adventures in a book titled "Memoirs," though the constant arrival of new events leaves its completion uncertain.

Moominpappa possesses a distinctive appearance: a round, white form resembling a bipedal hippopotamus, featuring a large snout and a thin, tufted tail. He almost always wears a black top hat, personalized inside with the inscription "M.P. from your M.M." to distinguish it, and frequently carries a black cane primarily for aesthetic reasons.

Dedicated to his family, Moominpappa occasionally experiences a secret longing for his former adventures or desires new experiences, like living among the Hattifatteners. This restlessness coexists with his honorable efforts to fulfill his duties. He is sociable, maintaining friendships with other adventurous characters in Moominvalley, including Wimsy and Stinky. According to his son, he possesses practical skills and can fix anything when motivated.