Tiamat

Tiamat, the Scaled Tyrant is the evil queen of dragons. She is a fearsome goddess of greed, envy, and hoarded wealth, and the patron of most chromatic dragons. She is the sworn enemy of Bahamut.

Appearance
Tiamat is depicted as a massive, five-headed dragon, with each head a different color of chromatic dragon, and her leathery wings spread poisonous clouds.

History
During the Age of Arcanum, Tiamat created one of the Arms of the Betrayers, given to her chosen champion of Ghor Dranas: the Will of the Talon, a war pick with the life force of a bone devil. One of the Vestiges of Divergence is also associated with Tiamat: the Wreath of the Prism.

Tiamat is imprisoned in Avernus, the first layer of the Nine Hells.

CelebriD&D with Joe Manganiello
Tiamat sent visions of a locked-away loop of golden thorns and gems to her follower Arkhan in his dreams. He sought out this artifact and, with the help of a group of mercenaries, eventually acquired the Wreath of the Prism from the Vault of Shumas in the Aggrad Mountains of Marquet.

Following the Chroma Crisis
For centuries, paladins of Bahamut had kept the worship of Tiamat limited to chromatic dragons, but after the Chroma Conclave emerged and attacked Emon, secretive humanoid cults sprang up. Some of the oligarchs of Tal'Dorei also covertly turned to Tiamat as their accumulated wealth was depleted.

In 835 PD, Calianna Mordsson, a sorcerer of draconic origins who escaped the Cult of the Caustic Heart, sought the help of the Mighty Nein to find and destroy an artifact that would allow ritualistic communication with Tiamat before the cult could acquire it. The adventurers did find the bowl in the possession of several merrow, and Yasha was able to destroy the magic item with Magician's Judge.

Known worshipers

 * Arkhan the Cruel
 * Cult of the Caustic Heart
 * Calianna Mordsson (formerly)
 * Serissa
 * The Chroma Council
 * Note: This is not the Chroma Conclave, which never considered itself subservient to Tiamat.
 * Hulil Lutan
 * Raegrin Mau