One Punch Man is a Japanese manga series written and illustrated by One. The series follows the story of Saitama, a superhero who has become bored by the absence of challenge in his fight against evil and seeks to find a worthy opponent.

Saitama is a bald, ordinary-looking man who gained immense strength after training himself to the point of near death. With his new powers, he quickly rose through the ranks of the superhero community and became known as One Punch Man, due to his ability to defeat any opponent with a single punch. Despite his overwhelming strength, Saitama is frequently overlooked and underestimated due to his unremarkable appearance.

The series follows Saitama as he searches for a worthy opponent and battles various villains and monsters, including the cyborg Genos, the ninja Speed-o'-Sound Sonic, and the monster Mosquito Girl. Along the way, he encounters other superheroes and villains, including the S-class hero Bang, the A-class hero Puri-Puri Prisoner, and the villainous organization the House of Evolution.

One Punch Man has gained widespread popularity for its unique blend of action, comedy, and satire. Its unconventional portrayal of the superhero genre and its subversion of common tropes has won the series a large and dedicated fan base.