Uncle Jam, called Jamu Ojisan in Japanese, is the creator and primary caregiver for Anpanman and other bread-based heroes. His story begins in the earliest picture books as a baker crafting Anpanman when a life star landed in his oven, cementing his foundational role in the series' mythology. This act connects to themes of sustenance and resilience, influenced by creator Takashi Yanase's wartime experiences with starvation, shaping Uncle Jam's purpose to alleviate hunger.

Physically, Uncle Jam resembles Anpanman but displays distinct age markers: gray hair, prominent fluffy eyebrows, a mustache, and lighter red cheeks and nose. He consistently wears a baker's uniform of a white chef's hat, shirt, pants, apron, and bluish-gray shoes. His personality blends profound kindness with extensive practical knowledge and ingenuity. Having traveled widely in his youth, he possesses broad world understanding reflected in his bakery's book collection. He demonstrates expertise not only in baking diverse breads and dishes but also in advanced mechanics, designing and constructing machines like the Anpanman Mobile, and repairing robotic characters.

His relationships center on paternal care and communal support. He nurtures Anpanman like a son, encouraging him from infancy to uphold justice and kindness; Anpanman typically addresses him by name. He maintains a close, non-familial partnership with Batako, collaborating on bakery operations and Anpanman's upkeep. Their relationship is deeply caring and familial, with official sources stating they are unrelated and Batako has been with him since infancy. He acts as creator and mentor to other heroes: offering father-figure support to Melonpanna, persistently inviting the conflicted Rollpanna to join the bakery, and fostering Creampanda's abilities like Anpanman's. His supportive role extends to allies like Shokupanman and Currypanman, assisting them despite ambiguous or retconned origins in their creation myths.

Within the narrative's internal logic, Uncle Jam and Batako are identified as fairies, clarifying their non-human status in a world without humans. His background and core attributes remain consistent across all media. His practice of baking replacement heads for Anpanman—shared to feed the hungry—symbolizes a rejection of scarcity and greed, reinforcing the series' message of mutual aid and the joy of living.