Tyrannus DracoRex (character)

Bahamut was was once a valuable ally to the Warriors of Light, he was only fighting for them to acquire godhood so he can end the timeless struggle between light and darkness on his own terms. When he became an Astral, Bahamut was immediately corrupted into the Tyrannus DracoRex, and is retroactively the ultimate antagonist of the Final Fantasy series as a whole.

Personality
Before his transformation into the God of War, Bahamut was an amoral, power-hungry dragon who delighted in the destruction of lesser life-forms, and kept his dark side very well hidden from the Warriors of Light(for over 30 years in real life). He sees himself as above the common conventions of good and evil and believes the ends justify the means, dismissing any alternate, more mutually acceptable solutions to any problem.

When he became the God of War by the events of Final Fantasy XV, Bahamut had finally lost all his moral light and became a truly evil, heartless monster who would destroy an entire planet just to get rid of all the daemons he despised; even though Bahamut ironically had a role in their creation, if not actually created himself. As the DracoRex, he devolved from a morally dubious keeper of order into a selfish, deceitful, hubristic, bloodthirsty, sadistic, uncompromising, hypocritical, spiteful tyrant who has no problem with sacrificing anyone to meet his goals.

Musical Themes
Tyrannus DracoRex's leitmotif of the same name is remixed from the final boss theme of Blue Dragon.