Uncle Jam, known as Jamu Ojisan, created Anpanman and other characters like Melonpanna, Rollpanna, and potentially Currypanman (though Currypanman's origin has conflicting accounts). His origin and role remain consistent across all media. Anpanman came to life when a "star of life" landed in Uncle Jam's oven as he baked an anpan, imbuing the bread with life. Physically resembling Anpanman but showing age, he has gray hair, fluffy eyebrows, a mustache, and lighter red tints on his cheeks and nose. He consistently wears a white chef's hat, white shirt and pants, a white apron, and blueish-gray shoes.

Profoundly kind, warm, and dedicated to helping others, Uncle Jam possesses extensive knowledge gained through youthful travels, reflected in the numerous books within his bakery. He is both an expert baker, capable of preparing diverse dishes, and a skilled mechanic who designs and constructs mecha machines like the Anpanman Mobile, while also repairing robotic characters. He operates the bakery, the central hub for the heroes, baking replacement heads for Anpanman and other bread-based heroes when their heads become damaged, dirty, or depleted from sharing, instantly restoring their strength and abilities. He maintains their flight-essential capes, though Batako typically handles repairs, and his mechanical expertise extends to inventing and maintaining vehicles and robots.

Uncle Jam shares deep familial bonds with his creations. He raised Anpanman from infancy, encouraging justice and kindness, establishing a father-son dynamic. He maintains a close, familial relationship with bakery assistant Batako; explicitly unrelated by blood, they care for each other like family, with some episodes suggesting Batako has known him since infancy. He acts as a father figure to Melonpanna and Creampanda, nurturing their abilities as he guided the young Anpanman. His relationship with Rollpanna is complex due to her dual nature (a red heart of goodness and a blue heart of evil caused by Baikinman's interference during her creation). Despite her tendency toward evil, he persistently invites her to join the bakery inhabitants, displaying a soft spot for her as his creation.

Within the series lore, Uncle Jam is not human, as the Anpanman World lacks humans; both he and Batako are explicitly identified as fairies despite their human-like appearances. Earlier manga depictions showed him smoking a pipe, omitted from the anime and subsequent adaptations.