Uncle Jam creates and cares for Anpanman and other bread-based heroes. His origin in the earliest picture books shows him as a baker crafting Anpanman when a life star landed in his oven during bread-making, imbuing the dough with life, establishing his foundational role. Physically resembling Anpanman but with age-related distinctions, he has gray hair, prominent fluffy eyebrows, a mustache, and lighter red tinting on his cheeks and nose. He consistently wears a white chef's hat, shirt, pants, apron, and blueish-gray shoes, emphasizing his baker identity.

His personality blends deep kindness with extensive knowledge and practical ingenuity. Widely traveled in his youth, he maintains a broad understanding of the world, reflected in his bakery's large book collection. He demonstrates expertise in baking diverse breads and dishes alongside advanced mechanics, designing and constructing mecha machines like the Anpanman Mobile. His mechanical skills also extend to repairing robotic or machine-based characters. Relationships center on paternal care and communal support. He nurtures Anpanman like a son, encouraging him from infancy to uphold justice and kindness; their bond reflects a father-child dynamic, though Anpanman typically uses his name. He maintains a close partnership with Batako, collaborating on bakery operations and Anpanman's upkeep, described as deeply caring and familial.

He acts as creator and mentor to other heroes: offering father-figure support to Melonpanna, persistently inviting the antagonistic Rollpanna to join the bakery community despite her dual-hearted nature, and fostering Creampanda's abilities similarly to Anpanman's upbringing. His role extends to allies like Shokupanman and Currypanman, whom he assists despite ambiguous or retconned origins in their creation myths. The character embodies themes of sustenance and resilience, influenced by the author's wartime starvation experiences. His practice of baking replacement heads for Anpanman—who shares them to alleviate hunger—symbolizes a rejection of scarcity and greed, aligning with the core message about mutual aid. Uncle Jam and Batako are identified as fairies within the narrative, clarifying their non-human status despite human-like appearances, as humans do not exist in this world. His background and attributes remain consistent across all official media, including seasons, movies, OVAs, and spin-offs. In films, his role aligns with established patterns of providing guidance and support within the bakery community while indirectly facilitating protagonists' interventions in conflicts.