Saitama is the protagonist of One Punch Man, a satirical superhero who can defeat any opponent with a single punch. After training so intensely that he lost all his hair, he gained limitless strength but also lost the thrill of battle. His bored, deadpan expression and simple costume of a yellow suit and red cape contrast humorously with his god-like power level.

Despite being the strongest being in his universe, Saitama struggles with everyday problems like making rent, finding worthy opponents, and getting recognition from the Hero Association that initially ranked him as a lowly C-Class hero. His friendship with the cyborg Genos, who becomes his devoted disciple, provides much of the series' heart. Saitama's character serves as both a parody of and love letter to the superhero genre, exploring what happens when someone becomes too powerful to find meaning in their abilities. His catchphrase "OK" and apathetic attitude have made him an iconic figure in modern anime.