Gorgons were three sisters Stheno, Euryale, and Medusa. Only Medusa was mortal, two others were immortal. They had snakes on the heads instead of hair, and one look at their faces turned anyone into stone. Perseus, a Greek hero, with the help of gods killed sleeping Medusa and cut off her head, which nevertheless continued to be dangerous and turn into stone anyone who dared to look at it.
See: Caravaggio Medusa.