Tiamat

Tiamat is the five-headed queen of the evil chromatic dragons. She has one head for each customary color of chromatic dragon (black, blue, green, red, white), and each head has the powers of a member of the respective race of dragonkind. Her body is a blending of various chromatic dragon forms with an appropriately multicolored hide. Her body also has traits in common with a wyvern, including a long tail tipped with a poisonous stinger.

Tiamat has also been known to manifest as a dark-haired human sorceress.

Tiamat was also one of the first deities to have aspects, or lesser avatars. These aspects may appear as powerful versions of her chromatic children or as versions of her own five-headed form.

Relationships
Like most other draconic deities, Tiamat is the offspring of the dragon creator deity Io. She is the eternal rival of her brother Bahamut, the ruler of the good metallic dragons. It is hinted that her overt hatred toward Bahamut has developed, over a vast period of time, into a twisted lust for her brother as well. She dwells in Avernus, the first layer of the Outer Plane of Baator (also known as the Nine Hells). The first edition of Advanced Dungeons & Dragons named her as the ruler of Avernus; later editions reserved the rulership of the layers of Baator for powerful baatezu (devils).

Three Baatezu nobles (granted to her by Bel) serve Tiamat and command her armies on Avernus. Malphas leads 40 companies of abishai, Amduscias leads 29 companies of abishai, and Goap leads three companies of erinyes.[25] With Pearza of the Dark Eight, Tiamat created the first abishai.

Tiamat presently has five consorts, who are great wyrms of each chromatic dragon species. Previous consorts include Apsu, Kingsu, Ephelomon, the red dragon Etiol, and the now-undead dragon Dragotha. Three of Tiamat's children were detailed in Dragon #260. An-Ur, the Wandering Death, wanders the Ethereal Plane, devouring whole demiplanes.[26] It supposedly sprang into being from Tiamat's "first breath", which may have been the name of one of her consorts, though An-Ur resembles no draconic species, except perhaps the ethereal moonstone dragons. Dhakoth the Corruptor was born on the Negative Energy Plane; its father is unknown. Mordukhavar the Reaver is the offspring of Tiamat and Cantrum of the Dark Eight. Kurtulmak is also her son, at least according to some myths.

Tiamat battles Bahamut, her Lawful Good counterpart. Heironeous and Moradin also consider themselves her enemies. Tiamat claims not to need allies, although she has many pacts with Bel and with lawful evil deities such as Hextor.

In 4th Edition, Tiamat is at war with Zehir ever since she first invaded his realm of Tytherion. While the two gods are not openly fighting right now, they are far from allies; the current situation can mainly be regarded as a temporary cease-fire.