Jam Ojisan created Anpanman when a shooting star struck an anpan baking in his oven, imbuing the pastry with life and cementing Jam Ojisan's pivotal role in his existence. He operates a bakery where he continually bakes fresh heads for Anpanman, essential replacements whenever Anpanman's current head weakens or sustains damage—often after he shares portions to feed hungry beings. During replacement, the old head detaches, and the new one restores Anpanman's strength and vitality.

Jam Ojisan holds vast knowledge spanning nearly all aspects of the world, maintaining a kind and supportive nature while directly aiding Anpanman's heroics through his baking. His assistant, Batako-san, works alongside him crafting and repairing capes for Anpanman and fellow heroes. A dog named Cheese resides at the bakery; the manga depicts Cheese becoming a loyal companion after Anpanman rescued him, while the anime shows a young Anpanman encountering Cheese on his first patrol and feeding him part of his head.