Styx was the river daughter of Okeanos and Tethys, the eldest of Okeanos, which was out of three thousand children. When Zeus was at war with the other Titans, He promised that any god or goddess who fought on his side would be rewarded justly. Styx and her children were the first ones to stand with Zeus. And of course, later on, she was rewarded to become known as The Oath River.

Disliked strongly by the immortals, Styx made her home in the underworlds. When a quarrel erupted on Olympus, Zeus would send Iris to Styx for a pitcher of water. Any immortal who poured the water of Styx. and swore an oath, is solemnly bound to tell only the truth. The punishment for breaking that oath is one year without air. If that is not enough, than for nine additional years they not allowed to attend any festivals nor share the company of the other immortals.