Step 1 : Introduction to the question "What three-headed mythological creature guarded the entrance to Hades?"
...One of the most well-known of Greek's mythological creatures is the three-headed dog who guarded the entrance to Hades. Cerberus had one job: allows the spirits of the dead to enter the underworld and allow none to leave. Cerberus was also a faithful servant to the god of the underworld Hades. The river Styx was the boundary between the underworld of the dead and the world of the living on Earth. Depictions of Cerberus often show him dutifully patrolling the banks of the Styx. Source: GreekGodsAndGoddesses.net
