Thousand-Year Evil

It is a mass of malignant energy that lives inside a wolf mask known as the Dark Mask, which was used 1,000 years ago by Shrogane in order to use its power to combine its three Power Animals in Gao Hunter and thus be able to kill the Ultimate Org Hyakkimaru. However, even though I managed to finish with the Org, the mask took full control of the body of Shirogane which ended up transforming it into the Duke Org Rouki, while transforming Gao Hunter into GaoHunter Evil, and its components in Demon Beast in the process. Unable to control, Shirogane had his allies seal him in a stone coffin.

Centuries later, is released by the Highness Duke Org Ura to fight against the Gaorangers, although in a prinicpio was able to remember who was, Ura implants a special grasshopper in him to modify his memory and preventing him to remember. Rouki is then defeated by the Gaorangers, who manage to defeat GaoHunter Evil to break the curse of the curse, freeing both Shirogane and his Power Animals from malign power in the process.Later, Rouki returns and tried to kill Shirogane for using his power. But he is finally defeated by the combined efforts of GaoSilver and Gaorangers and finally killed by GaoHunter Justice.

Although defeated, the Thousand-Year Evil within the mask is released and removed, with Ura cultivating it to be able to create powerful Orgs to fight against the Gaorangers, while giving the Duchess Orgs TsueTsue and Yaibaiba energy to transform them into their Armored Forms. After the last Org created by the evil energy was defeated, Ura captured Shirogane so that he readsorba the evil power to transform it again into Rouki. Eventually, Shirogane rejects power, which is then adsorbed by Ura allowing him to evolve into a more powerful form as he had planned from the beginning. With the power of the Thousand-Year Evil's dentor, Ura massacred the Gaoranger, leaving Kakeru and Shirogane as sole survivors. While trying to fight the strengthened Ura on their own, the other Gaorangers provide GaoRed the Falcon Summoner and GaoFalcon from the other world, while GaoGod revives them to help train GaoIcarus. After a battle armor, Ura is purged of the Thousand-Year Evil after being wounded GaoIcarus, returning it to its original form. Ura is wounded by GaoSilver and finally killed by the Hyakuujuuken of Gaorangers, destroying the Thousand-Year Evil forever, while Tsuetsue and Yabaiba return to their original form as a result.