Bagan, an ancient demonic monster from Chinese mythology, was discovered and awakened by a race of unnamed alien invaders. The aliens supercharged Bagan with both Godzilla and King Ghidorah's cells, causing him to grow to incredible size and become even more powerful. Bagan was unleashed in Tokyo to destroy Godzilla, and proved to be much too powerful for Godzilla to defeat alone. Thankfully, a group of scientists were able to supercharge Godzilla with some of King Ghidorah's cells, transforming him into Super Godzilla. In his new powered-up form, Godzilla was able to defeat Bagan, banishing the demon and forcing the aliens to retreat.
Bagan is incredibly powerful, and has greater physical strength and resistance to damage than even Godzilla. Bagan possesses a deadly Slasher Claw attack, he can create a Diamond Storm that he fires from his horns, he can spit a white Plasma Beam, and project a forcefield.
- In Reawakening of Godzilla, Bagan was to start out as three individual kaiju, the Doragon Reijuu (Sacred Dragon Beast), Enjin Reijuu (Sacred Ape Beast), and the Mizu Reijuu (Sacred Water Beast). After being defeated by Godzilla in each form, Bagan would transform into a totem-like composite of all three beasts and battle Godzilla again. In this form, Bagan would have been unable to regenerate, and would be destroyed by Godzilla for good.
- In Mothra vs. Bagan, Bagan was to be awakened by human activity and begin a campaign of destroying human civilization. Mothra would arise to stop him and battle Bagan across the planet before ultimately being killed, forcing her newborn larva to take on Bagan. The new Mothra would face and defeat Bagan in a final battle in Shanghai.
- Though Bagan never appeared in a film, his general backstory and some of his physical characteristics were used for the monsters Battra, Desghidorah, and Destoroyah.
- Bagan is the largest monster in the Godzilla franchise, standing at 150 meters (the same height as the Heisei King Ghidorah) and weighing 280,000 tons (80,000 tons heavier than the final form of Biollante).
- The word "Bagan" is Indonesian for "blueprint" or "draft," which is ironic considering Bagan was planned to appear in multiple films but ultimately scrapped.
- Bagan appears as a playable character in the fan-made flash game Godzilla: Daikaiju Battle Royale.