Hercules brought Cerberus back alive as the final labor in the traditional sequence.
Cerberus was the multi-headed guard dog of Hades, ruler of the underworld. Hercules was ordered to capture the creature and present it to Eurystheus without using weapons. Before entering the underworld, Hercules was initiated into the Eleusinian Mysteries in many versions, allowing him to learn how the living could enter and return.
Hades agreed to let Hercules take Cerberus provided that he subdued the dog without his usual weapons. Hercules overcame the beast through strength and brought it to the world above. Eurystheus was terrified and hid in a bronze vessel, then ordered Hercules to return Cerberus to the underworld. Cerberus is often pictured with three heads, although ancient descriptions and artworks vary in the number of heads and additional features.