In Greek mythology, Prometheus is a Titan, culture hero, and trickster figure who is credited with the creation of man from clay, and who defies the gods by stealing fire and giving it to humanity, an act that enabled progress and civilization. Prometheus is known for his intelligence and as a champion of mankind. The punishment of Prometheus as a consequence of the theft is a major theme of his mythology, and is a popular subject of both ancient and modern art. Zeus, king of the Olympian gods, sentenced the Titan to eternal torment for his transgression. The immortal Prometheus was bound to a rock, where each day an eagle, the emblem of Zeus, was sent to feed on his liver, which would then grow back overnight to be eaten again the next day. (In ancient Greece, the liver was often thought to be the seat of human emotions.) In some stories, Prometheus is freed at last by the hero Heracles (Hercules). In another of his myths, Prometheus establishes the form of animal sacrifice practiced in ancient Greek religion. Evidence of a cult to Prometheus himself is not widespread. He was a focus of religious activity mainly at Athens, where he was linked to Athena and Hephaestus, other Greek deities of creative skills and technology.