Many international fans of One-Punch Man can easily catch its parodies of superhero comics and shonen manga, but they might not know that it also draws inspiration from a children’s anime called Anpanman. Anpanman never took off in the West, but it's one of the highest-grossing media franchises of all time, generating over $50 billion in total retail sales revenue.
Created by Takashi Yanase as the hero of a series of children's books in the '70s, and subsequently starring in one of the longest-running anime of all time, Anpanman is a hero with a head made of bread, on a journey to protect the world from Baikinman (Bacteria Man). He does this with the help of his food-inspired friends, such as Shokupanman, Currypanman and Creampanda. He'll often feed those in need pieces of his own head.
Saitama obviously isn't made of food, but he does share many conspicuous traits with the much-admired children's hero. Both characters have powerful single-punches and simple character designs, not to mention their noticeably bald heads. Saitama's cape, belt, boots and gloves together also resemble Anpanman's costume. Perhaps the most direct connection between the two is that in Japanese, the title One-Punch Man is pronounced like Wanpanman, which makes the show's inspiration that much more obvious.
Both Anpanman and One-Punch Man are decidedly silly takes on the superhero genre. Whereas Anpanman uses a goofy character design to be accessible for kids, One-Punch Man uses a similar character design to present itself as satirical for adults. Considering his unparalleled strength, one would expect Saitama to have been based on a god or some really powerful creature -- taking inspiration from a talking piece of bread is so unexpected that it's funny.
The two series also share plot similarities -- both heroes find themselves punching away aliens and saving the day. Of course, the plots can't be that similar -- Anpanman is a show aimed exclusively at young children, with all the simplicity that entails, while One-Punch Man is aimed at adults and can get into more violent and complicated narratives surrounding its seemingly one-joke hero.
Anpanman is happy, helpful and reliable. Saitama is all of those things as well -- sometimes. ONE has given Saitama some very non-heroic attributes, most significantly a general sense of apathy. Saitama may be the world's strongest superhero, but he most definitely isn't the world's best role model.