In Greek mythology, Cerberus, son of Typhoon and Equidna, was the guardian in the gates of Hades, the realm of the dead. In appearance, Cerberus was a gigantic size of a dog, which had three heads (or 50 according to different versions), a snake tail and on his back and thick layer of snakes heads. Its mission at the gates of the kingdom of the dead was to prevent any alive human being infiltrate in Hades realm, if needed, killed anyone who tried.
Only two person who able to go through Cerberus. First is Orpheus, who play beautiful music that able to sleep the dog and and step through into Hades to rescue his beloved, Eurydice. And Hercules, one of the twelve work given by commissioned Euristeus who must take Cerbero to Micenas. Once such a feat, Hercules was forced to return to the gates of Hades, because Euristeus was petrified to see such horror in his eyes. In Final Fantasy series, Cerberus appear as summon in Final Fantasy VIII and often appear as mob monster.