Istishia

Istishia, also known as King of Water Elementals, is the neutral primordial deity of elemental water and purification.

Divine Realm
Though Istishia does not have a court in the conventional sense, and despite his followers belief that he encompasses the whole Elemental Plane of Water, he does maintain a distinct divine realm on that plane within the Great Wheel cosmology called Sea of Timelessness.

Worshipers
Istishia is worshiped by Sailors, Pirates, Water Elementals, Water Genasi, some Aquatic Elves, and others who feel a bond with the Ocean's destructive power.

Worship in Zakhara
On the continent of Zakhara, Istishia is called one of the cold gods of the elements. As those are seen as uncaring for human affairs, they are considered opposed to the Land of Fate's pervasive culture of Enlightenment. Only a few Zakharans are willing to worship a cold god in order to gain power.

Relationships
Istishia allies are those deities with a relation to water, like Deep Sashelas, Eldath, Valkur, and Umberlee, but they are not strong relationships. He opposes Kossuth in every way. Istishia sits back and watches the struggle of the archomentals of water, Ben-Hadar and Olhydra; presumably he would intervene if one would achieve a real chance to get control of elemental water.

Advanced Dungeons & Dragons 1st edition (1977-1988)
Ed Greenwood initially used Straasha, one of Moorcock's Elemental gods as found in the original Deities & Demigods, as the elemental lord of water for his home Dungeons & Dragons campaign set in the Forgotten Realms. As Greenwood indicated in his article "Down-to-earth Divinity" in Dragon #54 (October 1981), Moorcock's elemental gods "may later be replaced in [his] universe by 'official' AD&D beings as these are published". Istishia first appeared in the original Manual of the Planes (1987), and was featured as one of the elemental lords for the Forgotten Realms in the Forgotten Realms Campaign Set's "Cyclopedia of the Realms" booklet (1987).

Advanced Dungeons & Dragons 2nd edition (1989-1999)
Istishia was described in the hardback Forgotten Realms Adventures (1990), the Forgotten Realms Campaign Setting (1993) in the "Running the Realms" booklet, and Faiths & Avatars (1996).

Dungeons & Dragons 3rd edition (2000-2007)
Istishia appears as one of the major deities of the Forgotten Realms setting again, in Forgotten Realms Campaign Setting (2001), and is further detailed in Faiths and Pantheons (2002).

Dungeons & Dragons 4th edition (2008-Present)
Istishia appears in the fourth edition as a primordial.