In Greek mythology, Styx ( ; Ancient Greek: Στύξ ] ) is a deity and a river that forms the boundary between Earth and the Underworld (the domain often called Hades, which also is the name of its ruler). The rivers Styx, Phlegethon, Acheron, Lethe, and Cocytus all converge at the center of the underworld on a great marsh, which sometimes is also called the Styx. According to Herodotus, the river Styx originates near Feneos