Tathamet is a seven-headed dragon of pure evil and all that is vile. It was known as the Prime Evil and was created as a result of being cast off of all the dark attributes within Anu long before Sanctuary came into existence.
Separated from one being, Tathamet and Anu were both trapped within the same place and they battled with each other for an indefinite length of time. Eventually, the evenly matched adversaries destroyed each other, causing the universe to come into being.
In Diablo III, Tathamet makes his first in-game appearance in the reincarnated form of Diablo (who in turn used Leah's body for this purpose). Tathamet is later defeated by mortal heroes after the near-destruction of the High Heavens.
- Tathamet is most likely named after Tiamat, a chaos monster and the primordial, draconic goddess of the oceans from Babylonian mythology. Tiamat mated with Abzu, the god of fresh water, giving birth to the gods; this parallels the clash of Anu and Tathamet creating the universe. Tiamat is later killed by Marduk, and her divided body form the heavens and the earth, like how Tathamet's body became the foundation of the Burning Hells.
- Tathamet's depiction as a seven-headed dragon is likely influenced by the dragon, the second of the two beasts of Revelation, who together bring about Armageddon. There are other myths in mythology throughout the Middle East depicting a seven-headed dragon or serpent as an evil being of destruction.
- The relationship between Anu and Tathamet may be based on Ahura Mazda and Angra Mainyu of Zorastrianism. Ahura Mazda, the counterpart of Anu, was the original "uncreated" god who created Angra Mainyu, the counterpart to Tathamet, by purging himself of all his evil. Just as Tathamet is a being of destruction and the "father/grandfather" of all demons, Angra Mainyu is a being of chaos and destruction who created demons to battle Ahura Mazda.
- Tathamet's heads birthing the Great Evils is likely influenced by the Ogdru Jahad of Hellboy by Dark Horse Comics. The Ogdru Jahad are seven evil entities referred to collectively as "the Dragon", among other names, and birthed 369 children known as the Ogdru Hem, who represent the archetypical "demons" in Hellboy lore.
| Prime Evil — Tathamet|
Prime Evils — Diablo • Mephisto • Baal
| Supreme Creator — Anu (Tathamet)|
Askari Pantheon — Athulua • Hefaetrus • Karcheus • Kethryes • Lycander • Philios • Zerae
Barbarian Pantheon — Bul-Kathos • Korlic • Madawc • Talic
Rathman Pantheon — Trag'Oul
Sahptev Pantheon — Inna
Umbaru Pantheon — Giyua
Vecin Pantheon — The Allmother