Bahamut

Bahamut was a Elder Primal created from the draconic ancestor of the Dravanian Horde to fight against the technomancers of Allag during the Third Astral Era. It was defeated by the weapon Omega and eventually incarcerated by Emporer Xande inside Dalamud, an artificial satellite orbiting the planet. Xande intended to use Bahamut's energies to forge a covenant with the Cloud of Darkness that would enable him to conquer all of Hydaelyn. Xande's hubris only resulted in cataclysm that destroyed the Allagan Empire and ushered in the Fourth Umbral Era.

Dalmud's origin as an Allagan structure was lost over time with most Eorzeans believing, until after its destruction, that it was a naturally created moon. Nael Van Darnus of the Garlean Empire, knowing the truth about the moon, created Project Meteor as a plot to wipe out Eorzea's Primals, disregarding the effect it would have on the realm's other inhabitants. By the time the Battle of Carteneau occured, Bahamut was freed. Driven mad after eons of incarceration, Bahamut unleashed his wrath upon the realm, setting off the great cataclysm known as the Calamity.

Louisoix and the Circle of Knowing attempted to recapture Bahamut in a new, Dalamud-like structure. At the last moment, Bahamut unleashed a Terraflare that tore apart Louisoix's magic and caused chaotic aetheric energies to instantly terraform Eorzea. Bahamut disappeared in the chaotic aftermath.