Hatabou is a recurring character from the Mr. Osomatsu series, whose origins trace back to the original Osomatsu-kun manga. His name, which means "flag boy," was chosen through a reader contest, and his most defining physical feature is the small Hinomaru, or Japanese flag, that protrudes from the top of his skull, though this flag has appeared in other contexts as well, such as a communist red flag or a skull and crossbones. He has a shaggy, bowl-cut hairstyle reminiscent of a kappa, a single bucktooth, and distinctive vertical lines under his nose that represent dried mucus. In his appearance in Mr. Osomatsu, he is depicted as an adult who has the same stature, childlike appearance, and voice as he did when he was young, often seen wearing green overalls over a light yellow hoodie and riding a tricycle.

In terms of personality, Hatabou is simple-minded, naive, and kind-hearted, often described as a baka-type, or foolish, character. He tends to wander aimlessly and lacks a deeper understanding of the world around him, living vaguely and courageously. Despite his general innocence, some depictions grant him a more severe or unsettling streak, particularly in his role as a wealthy CEO. This is most notable in Mr. Osomatsu, where he is initially introduced as an obscenely rich information broker known as Mr. Flag, having amassed a fortune through a combination of luck and happenstance rather than any particular skill or intelligence. His success is shown to be highly valued by powerful figures, yet his employees eventually revolt, recognizing his business incompetence, and he loses his entire fortune. After this downfall, he reverts to a more innocuous and gentle persona. A later, darker storyline implies that he begins selling "mystery meat" from food trucks, which is heavily suggested to be sourced from his former employees who betrayed him.

Hatabou's role in the story is that of a supporting character and a childhood acquaintance of the Matsuno sextuplets. The brothers are invited to his birthday party, where they discover his immense wealth, leading to a range of reactions from amazement to jealousy. He remains unbothered by his wealth and is shown to be generous, offering to let the sextuplets take as much money as they want from his vault. He treats the brothers as friends and is generally well-disposed towards them, even as they try to take advantage of his good nature. His key relationships include Chibita, who is sometimes his friend and sometimes his rival and bully, and Dekapan, who occasionally acts as a father figure or mentor. He also has family members, including an older brother who is notably a genius and a younger sister who also has a flag on her head.

Throughout his history in the franchise, Hatabou has been portrayed in many different ways. He can be a helpless victim, a cunning antagonist, a heroic figure, or a successful but clueless businessman. His intelligence fluctuates across adaptations, sometimes being depicted as sharper and other times as entirely foolish. One consistent trait is his habit of ending his sentences with the verbal tic "da jo" or simply "jo." Among all the characters in Mr. Osomatsu, he is arguably the most financially successful at his peak, and he is known for being one of the kindest to the Matsuno brothers, continuing to see them as friends even after his rise and fall in status.