Hercules was an extremely strong man and was always portrayed in peak physical condition in ancient art. He was sometimes shown with a beard, and very often, statues portrayed him with disproportionately large hands and feet.
Hercules' strength came from his father Zeus, the ruler of all gods. Hercules was a demigod, meaning he was half human and half god. This accounts for his strength and muscular appearance, but identifying an image of Hercules can be difficult since there are other types of muscular "stock characters" in the repertoire of ancient art, such as the athlete.
A clear indicator of whether a subject in ancient art is Hercules is his attributes. Attributes are objects that accompany images of gods and demigods to clarify the subject's identity. Hercules' attributes were a rough-looking club and a lion skin, which he wore after completing the first of his twelve labors. These two objects were completely unique to Hercules, and no other character was ever shown with them.
Depictions of Hercules often show his twelve labors. The most commonly used labors in ancient art are those in which Hercules killed the Nemian lion, slayed the hydra, seized the Erymanthian boar, drove away the Stymphalion birds and captured Cerberus.