Which river goddess was the first to ally with Zeus in the Titanomachy? Styx was the first deity said to join Zeus.
Styx was both an underworld river and its personified goddess. In the usual genealogy, she was the eldest Oceanid, daughter of Oceanus and Tethys. She married the Titan Pallas and became the mother of Nike, Zelus, Kratos, and Bia—personifications of victory, zeal, strength, and force.
When Zeus called the gods to choose sides against Cronus, Styx followed her father Oceanus’s advice and arrived first, bringing her children with her. Zeus rewarded her loyalty by making Styx the sacred oath of the gods. Divine beings who broke an oath sworn by Styx faced severe punishment and temporary exclusion from the company of the gods.
Styx is often reduced to simply being a river in Hades, but Greek myth treats her as both a place and a divine person. She is also distinct from Acheron, Cocytus, and Lethe, the other famous rivers associated with the Underworld.