CERBERUS
Cerberus is a three headed dog who waits at the gates to the Underworld. He was a very vicious and scary dog who even the gods feared. They were there to keep people in line while waiting to get in the Underworld.
http://www.factmonster.com/biography/var/cerberus.html (Cerberus)
http://www.factmonster.com/biography/var/cerberus.html (Cerberus)
http://www.thanasis.com/cerberus.htm (Photo Credit)