Jam Ojisan, also called Uncle Jam or Mr. Jam, created Anpanman and lives in a bakery within their world. He accidentally brought Anpanman to life when a "star of life" fell into his oven during anpan baking, marking Anpanman’s birth. This event established Jam Ojisan as a paternal figure who raised him from infancy.

He has gray hair, fluffy eyebrows, a mustache, and light red cheeks and nose, setting him apart from Anpanman. He consistently wears a white chef’s hat, shirt, pants, and apron with blueish-gray shoes. Profoundly kind and warm, Jam Ojisan possesses extensive knowledge from youthful travels. He is an expert baker and cook who prepares diverse dishes, while also excelling as an inventor and mechanic. He constructs mecha machines like the Anpanman Mobile and repairs robotic characters.

As a father figure, he maintains close bonds with bread-based heroes he created or supported, including Melonpanna, Rollpanna, and potentially Currypanman—though the latter’s origin remains ambiguous later. He mentors characters like Creampanda and fosters Melonpanna’s development. His relationship with bakery assistant Batako is familial despite no blood relation; they share deep mutual care, with hints of their association dating to her infancy. Jam Ojisan repeatedly invites unstable Rollpanna to join the bakery family, caring for her despite her "evil blue heart."

The Anpanman world lacks humans; Jam Ojisan and Batako are considered fairies despite human-like appearances. Early manga depicted him smoking a pipe, omitted in adaptations. His name was unspecified in the original 1973 picture book, referred to simply as "uncle" or "old man." His legacy includes generating over 1,768 characters, earning a Guinness World Record for the largest animated franchise ensemble.