Cerberus was the three-headed “Hound of Hades” that guarded the gates of the underworld in Greek and Roman mythology.
As the last of his 12 Labors, Hercules was required to capture Cerberus without using weapons and without harming the hellhound. Hercules accomplished the task by using his impenetrable lion-skin (taken from the Nemean Lion, the first of his labors) as a shield, and wrestling Cerberus until he submitted.
This sculpture of Cerberus is by Bernini, and is part of the large marble sculptural group The Rape of Proserpina, which depicts the abduction of Proserpina by Pluto, God of the Underworld and master of Cerberus.
Cerberus (1826) by William Blake: