Styx

In Greek mythology, Styx (/ˈstɪks/; Ancient Greek: Στύξ [stýks]; lit. "Shuddering") was 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.