Humans

Humans (人間, Ningen) are the dominant race in the world, as they outnumber all other races.

Overview
Humans, also known as  Homo sapiens (ホモサピエンス, Homosapiensu) are a race of sapient bipedal primates that inhabit the world of One-Punch Man. They are the dominant and most abundant species of animal on the planet.

Human size vary according to it's ethnicity and age. Humans possess skin color which ranges in variety from the darkest brown to the lightest hues. Certain body parts, mostly facial structures of humans vary a lot from ethinicty and age.

Plot
Humans appeared on the world in an unknown period of time. They were the dominant species in the world prior to 15 years ago, when a race of creatures labbeled Mysterious Beings appeared and started creating havoc and killing humans. At first they could be easily dealt with, but with time Mysterious Beings grew stronger in power to the point regular weapons became useless against them. In order to fight the Mysterious Beings, the Hero Association was created.

Abilities & Powers
Humanity's main power is their intelligence and numbers. They vastly outnumber the Mysterious Beings and possess advanced technology which allowed them to multiply across the planet. Whomever, most of the weapons they use prove to be useless against stronger Mysterious Beings. Humans defend themselves from many of the stronger Mysterious Beings with the stronger than average human heroes from Hero Association. Mysterious Beings ranked as wolf and tiger are still dealt with using regular weapons.

'''The following section contains webcomic spoilers. You have been warned, manga-only readers.'''

According to Dr. Genus, every human is born with a natural limit. Once this limit is surpassed, a human gains the potential to manifest incredible power.

Trivia

 * It's hinted by both Tatsumaki and Dr. Genus that Saitama's powers were granted by breaking his human limits.