Zartra

Lady Zartra was once the most trusted advisor to the Atlantean warlord Attuma.

Avengers Assemble
After the break-up of the Cabal, Zartra switched sides and joined the resistance movement against Attuma. She sent one of her soldiers to the surface world to buy the Serpent Crown from Hydra so she could take control of Giganto and overthrow Attuma.

The Avengers initially opposed her, but after discovering her intentions, helped her into defeating Attuma. In the end, Zartra decided the Serpent Crown was too powerful for anyone, and threw it to the depths of the ocean, even though it was later secretly recovered by Hawkeye.