Euryale is one of the Gorgon sisters. Despite having faded earlier, Gaea revived her at some point. She appears in The Son of Neptune.
She, along with her sister Stheno, had been repeatedly killed by Percy, but they just kept on reforming. She scolds her sister for telling Percy the secret of Gorgon blood and for being too obsessed with her work, her hair is all coral snakes.
Compared to her sister, Euryale is much more determined and narrow minded.