In Greek mythology, Styx, also called the River Styx, is a goddess and river of the Underworld. Her parents were the Titans Oceanus and Tethys, and she was the wife of the Titan Pallas, and the mother of Zelus, Nike, Kratos, and Bia. She sided with Zeus in his war against the Titans, and because of this, to honor her, Zeus decreed that the solemn oaths of the gods be sworn by the water of Styx.

In Greek mythology, the Greek underworld, or Hades, is a distinct realm where an individual goes after death. The earliest idea of afterlife in Greek myth is that, at the moment of death, an individual's essence (psyche) is separated from the corpse and transported to the underworld. In early mythology the dead were indiscriminately grouped together and led a shadowy post-existence; however, in later mythology elements of post-mortem judgment began to emerge with good and bad people being separated.