The Styx is a river in Greek mythology that formed the boundary between Earth and the Underworld. The rivers Styx, Phlegethon, Acheron, and Cocytus all converge at the center of the underworld on a great marsh, which is also sometimes called the Styx.
POSEIDON - He is one of the twelve Olympian deities of the pantheon in Greek mythology. His main domain is the ocean, and he is called the "God of the Sea". Additionally, he is referred to as "Earth-Shaker" due to his role in causing earthquakes.
Grim Reaper: "Cerberus and Persephone," by Laura Csajagi, at deviantART. In Greek myth, the three-headed dog Cerberus ("Spotted") guarded the of the The Persephone ("Corn Striker" or "Death Bringer") was the wife of the Underworld Hades.