“The Empire lies in ruin, but that does not mean it is the end. We are the ones that live through the ashes, and keep them from dispersing. Through our efforts, the Empire will rise again!”―Centurion Claudius
The Imperialium is a secret organization, deployed after the decimation of the Imperials by Stormcloak rebels after the civil uprising in Skyrim. Since the signing of the White-Gold Concordat that is devoted to the protection of the Empire of Tamriel, the need for a secure branch if the main forces ever failed was needed. Formed by Claudius Maximilian, the Count of Cyrodiil, and Kaisarus Mede, the Prince of Cryodiil, the Imperialium seeks to safeguard the Empire from a variety of threats, both internal and external. They do this in the hopes of returning the Empire to its former glory, like they have successfully done many times earlier. While the Imperialium fights several enemies, they consider the Stormcloaks to be their primary foe.
Following the end of the Great War with the Aldmeri Dominion, there were many that did not want peace. These individuals had suffered terribly during the war at the hands of the Thalmor, often having been personally wronged, or having lost loved ones. As a result many objected to the White-Gold Concordat, and wanted to restrain and reinforce the legion incase another tragic defeat occurs. Others were dissatisfied for a different reason. They saw what the Great War and the White-Gold Concordat had done for the Empire. The Empire, which had once been strong was now a shadow of its former self, and it often bowed to the wishes of the Thalmor to avoid war. These individuals saw the Empire losing its soul, and heading gradually towards ruin. Among those who belong to both groups was Claudius Maximilian, the Count of Cyrodiil. He had lost his brother, and his brother's family to the Thalmor. Furthermore, he realized that if the empire continued to give ground to their enemies, and allow them to corrupt the politics and values of the Empire, it would eventually collapse. Determined not to see this happen, the Count gathered support from others that wished to continue resisting oppression, and formed a secret organization, the Imperialium.
While the Imperialium managed to remain a secret to most throughout Skyrim, the Stormcloaks slowly became aware of this covert group that was attempting to foil their en-devours. They chose not to bring the group to the attention of Ulfric or the Stormcloak military, as they felt concern that public knowledge of the group might inspire others within the rebelion to turn on themselves. The Imperialium used their right to travel through the Empire's territory to hunt down Talos worshipers to fight a covert war against the group, much like they had with the Blades. While the Stormcloaks were moderately successful, the scope and internal organization of the Imperialium escaped them. This lack of knowledge allowed the Imperialium to continue its work even with the pressure from the Stormcloaks.
Claudius proved himself skilled in matters of politics, business and espionage. On the surface he disguised himself as was one of the Stormcloaks. Although he was one of the biggest lieutenants within the rebellion, secretly he sought to undermine them at every turn. Under his leadership the Stormclocks suffered while the Imperialium grew, becoming better organized, funded and equipped. The Imperialium had agents and informants throughout Tamriel, and even integrated into the rebels after the war. Claudius even managed to cultivate assets within the Aldermi Dominion itself. To protect his identity, Claudius took the code-name Istar Cairn-Breaker while acting in his secret role as a powerful Stormcloak leader. However, in the end, his plot was discovered as Galmar Stone-Fist and Ulfric Stormcloak became aware of the Imperialium.