She is voiced by Kathleen Barr.
Eris is the sister of Queen Calissa. When Calissa and Eris were young, it was time for the Changing of the Tides Ceremony and only one could take the throne. Princess Calissa was more kind and fair than her sister, plus she could spin Merilia, whereas Eris couldn't, so she took the throne. Eris started to hate her sister.
After years, Eris overthrew Calissa and took the throne. She ruled Oceana for 15 years selfishly. The ocean became sick since the Merillia was unhealthy, as Calissa was unhappy locked up. But when Queen Calissa's half-human, half-mermaid daughter (Merliah) came to Oceana, Eris was deposed.
She later escaped from her prison with the unwitting help of Kylie Morgan. Eris revealed she had the power to make anyone live through their worst nightmare, and with it, she planned to take the thrown of Oceana and spin Merillia. Ultimately, she was defeated and experienced her worst nightmare, having legs instead of a tail.
Eris is vain and loves power and attention. She is the only one in the royal family who cannot spin Merilia (the life force of the sea), and that makes her jealous. She gets very angry when someone doesn't listen to her. Whoever displeases her, she throws them into an orange magical whirlpool that sends them to her dungeon.
In the end, her whirlpools are what finally got rid of her. In the sequel, she is capable to make nightmare spells, who make the worst fears of others come true. She is also a good actress being able to act nice. She can make powerful whirlpools by spinning her finger (normal sized) or swimming round and round at a fast speed (giant sized).
Eris has short reddish brown hair with orange streaks. She has dark brown eyes. Her mermaid tail (which in the end of the sequel is turned into human legs by one of her own nightmare spells), and on top has streaks of orange tones. She wears a big red headdress with a golden crown, and wears spiked earrings, golden bracelets and a red protective necklace that is thrown and broken by Merliah to show the inhabitants of Oceana that Calissa is alive. The red protective necklace was one of the things needed for Merliah to overthrow Eris. In the novel, when her tail was turned into legs, the bottom part of her clothes were turned into a torn dress while in the movie, they were turned into the bottom part of swimming trunks.