Queen Azshara

Queen Azshara was the beloved queen of the Night Elves 10,000 years ago and was one of the main causes of the War of the Ancients. She tried to bring Sargeras to Azeroth via a portal in order to become his wife, seeing him as the only being worthy of her. After the Burning Legion was defeated and the portal was destroyed, the Sundering occured and seeing the waters of the Well of Eternity entered her palace, used her powerful magic to shield herself and those in the palcae she resided in. However, she kept hearing voices offering her a chance at survival. She accepted and she and all who resided in the now sinking palace became the first Naga, with Azshara becoming their queen, becoming a hideous monster reflecting the evil that was always in her. It is possible the voices were that of the Old Gods, most likely N'Zoth.

She was a very powerful mage, such that only the very strongest members of the Burning Legion could have matched her. She had since grown in power thanks to the Old God's influence. She may even be more powerful than Deathwing himself.

She will be fought in the Well of Eternity instance in patch 4.3, though she won't be killed.