Naga Summoners are naga who Illidan made ethereal to better protect them, when they were continuing the spell Illidan cast using the Eye of Sargeras to destroy the Frozen Throne. They were stopped and the Eye of Sargeras was destroyed by the combined forces of the Sentinels and the Alliance (elven faction) in the The Ruins of Dalaran.
Since the summoners were ethereal, the Sentinels were forced to use magical attacks and spells to harm the summoners. Each of the Naga Summoners were killed by Archdruid Malfurion Stormrage, Warden Maiev Shadowsong, Prince Kael'thas Sunstrider, and an unknown human paladin (if he was rescued).
Naga Summoners can be placed on a map. They share the same combat abilities as their normal brethren, only having a slightly altered model and having a unique spell, which is purely cosmetic.