Styx

In Greek mythology, Styx (/ˈstɪks/; Ancient Greek: Στύξ [stýks], meaning "Shuddering") is both a goddess and one of the rivers of the Greek Underworld. She was the daughter of the Titans Oceanus and Tethys, and the wife of the Titan Pallas. Styx was the mother of Zelus, Nike, Kratos, and Bia. During the war between the gods and the Titans, she sided with Zeus, and in gratitude for her loyalty, Zeus honored her by decreeing that the gods must swear their most solemn oaths by the waters of Styx.