This twenty-year-old museum piece was the first military mobile suit, and is the common ancestor of both the Gundams and Oz's own mobile suits. Oz deemed the prototype Tallgeese too expensive to mass-produce and too hard to pilot, so the design was simplified and scaled down to create the standard Leo. As a result, the Tallgeese's specifications are superior to those of most modern mobile suits, and this mothballed prototype is the only thing in Oz's arsenal capable of fighting a Gundam. However, its high acceleration and instability make flying the Tallgeese hazardous for even the best of pilots.

The twin brother of Treize Khushrenada's Tallgeese II, this recreation of the legendary mobile suit was built at the very end of the great war between Earth and the space colonies. Its special weapons - a mighty mega cannon, and a heat rod derived from that of the Gundam Epyon - weren't completed in time for the Tallgeese III to see combat. After the war, it was seized by the Earth Sphere United Nation's intelligence agency, "Preventer." Though almost all mobile suits were destroyed by the new government in the name of world peace, the Tallgeese III was stashed away in case of emergency... an emergency that has now arisen.

This mysterious mobile suit is created by OZ leader Treize Khushrenada, based on data from the Tallgeese and the other Gundams. In keeping with Treize's philosophy, the Gundam Epyon eschews cowardly long-range weapons in favor of chivalrous close combat. Its main weapons are a segmented, whip-like heat rod, and a powerful beam sword whose energy is supplied by a direct connection to the Epyon's generator. The Epyon can also transform into a "mobile armor" mode for high-speed flight.