Ulkair is an incredibly powerful Great Unclean One, a Greater Daemon of the Plague God Nurgle. Ulkair manifested on the world of Aurelia in the M40 40th Millennium when a Warp Storm engulfed that planet, but he was defeated by the Blood Ravens Space Marine and Librarian named Azariah Kyras. But Aurelia was consumed by a Warp Storm and over the course of their mutual imprisonment Ulkair corrupted Kyras to Chaos, ultimately returning him to realspace to reunite with his Chapter and begin the process of corrupting the Blood Ravens to the service of the Ruinous Powers and heralding the return of Ulkair himself. Ulkair's plans were ultimately disrupted only through the heroism of Captain Gabriel Angelos and his fellow Blood Ravens Loyalists.
The Greater Daemon known as Ulkair has been a blight upon Mankind since ancient times. During the 40th Millennium, the Imperial world of Aurelia, located in the Aurelian Sub-sector of the Korianis Sector, was engulfed in a prodigious Warp Storm. The resulting turbulence pushed the planet out of its natural orbit, causing its environment to plunge into an unnatural and unexpected Ice Age. The world became entirely engulfed in ice as the temperatures plummeted, turning Aurelia into a frozen planetary wasteland referred to by Imperial astrocartographers as an Ice World. Much of its population died as a result of the sudden frigid environmental changes. Azariah Kyras was a Librarian of the Blood Ravens Space Marines Chapter serving alongside his master Moriah, the Chief Librarian of the Blood Ravens. When Ulkair manifested on the doomed planet during the Warp Storm, he was confronted by Moriah, who managed to wound the Greater Daemon before dying from his own mortal wounds. Kyras proved luckier and managed to defeat Ulkair, imprisoning the immensely powerful daemon on the frozen planet. Then the Warp took the world and Azariah Kyras along with it.
Ulkair remained trapped within his prison for over 1,000 standard years until the Black Legion Chaos Space Marines invaded Sub-sector Aurelia in the late 41st Millennium, led by their thrice-damned leader the Chaos Lord Eliphas the Inheritor, a former Dark Apostle of the Word Bearers who had been restored to life by the Chaos Gods to gain his vengeance upon the Blood Ravens. The Black Legion was intent on releasing Ulkair from his imprisonment so that he could pursue his wrath upon the people of the sub-sector.
Elsewhere in the Aurelian Sub-sector that they were responsible for protecting, the 5th Company of the Blood Ravens Chapter found themselves tasked with the dangerous mission of exploring and clearing an infested Space Hulk known as the Judgment of Carrion. The 5th Company took serious losses from the groups of Tyranids and daemons that infested the Space Hulk. Azariah Kyras suddenly appeared amidst his fellow Blood Ravens on the Hulk and used his psychic abilities to aid Apothecary Galan, the remaining ranking officer in the company, in defending the surviving Battle-Brothers from the Hulk's hideous inhabitants. The remains of the 5th Company, despite Kyras' aid, were still trapped on the Space Hulk, and unable to get back to their Thunderhawk gunships and escape.
At the same time, Galan found himself haunted by a malignant daemonic presence that Kyras identified as Ulkair, the Greater Daemon that the Blood Ravens had suffered terrible losses imprisoning a thousand years before, and which had caused Kyras to be lost in the Warp for centuries. Unbeknownst to his Battle-Brothers, Kyras had been corrupted by Chaos during his long imprisonment in the Warp with the Greater Daemon. He sought to corrupt his fellow Blood Ravens by enhancing their despair and playing on their fears. To gain the escape of the 5th Company from the Judgment of Carrion, Kyras entered into a pact with Ulkair in which in return for the Blood Ravens' escape from the Space Hulk, Galan agreed to be possessed by a daemon. When the 5th Company escaped, both Kyras and Galan were hailed as heroes of the Chapter and Kyras was welcomed back into the fold as a lost Battle-Brother.
When the Black Legion invaded Subsector Aurelia, Eliphas and his minions captured several Space Marines and then sacrificed them, in order to free Ulkair form his infernal prison. The arcane ritual freed the Greater Daemon as well as restoring Aurelia to realspace, enabling the daemon lord to manifest within the disease-ridden body of a Plague Marine which served as his Daemonhost. Once Ulkair successfully freed himself from his imprisonment, the newly returned Ice World of Aurelia was torn asunder. In the meantime, a Blood Ravens strike force led by Force Commander Aramus were tasked with the difficult mission of defeating the daemon lord before it launched itself across the sub-sector, threatening the existence of all the worlds used by the Blood Ravens to recruit the Chapter's Aspirants.
Aramus formed an alliance with Captain Gabriel Angelos and his men in order to successfully achieve their objectives. But first the Blood Ravens had to face the vile Chaos Lord Eliphas and his Traitor Marine minions. They clashed upon the world of Aurelia at the ruins of Keep Selenon. It was there that Aramus fought the Inheritor in single combat. Eliphas exhibited tremendous Chaotic powers and unmatched savagery against the hated servants of the "Corpse Emperor." The favour of the wretched Chaos Lord with the Dark Gods was such that he was able to call upon the personal blessings of all the Chaos Gods to aid him in battle. Despite his formidable might, the Blood Ravens overcame Eliphas, but before he could be slain he escaped their wrath by fleeing into the Warp. After Force Commander Aramus managed to fight his way through the remaining Forces of Chaos on Aurelia, he eventually confronted the Great Unclean One itself. After a long and hard-fought battle, Ulkair was once again defeated and imprisoned as Aurelia was cast back into the Empyrean, but remarked to the Blood Ravens that his prison was now inadequate and weakened, and that he would soon rise again to utterly destroy the Blood Ravens. The Astartes also had to deal with the new reality that their Chief Librarian and Chapter Master, Azariah Kyras, was a Traitor to the Imperium and a servant of Chaos.
Throughout the next decade, and the events of the Third Aurelian Crusade, Ulkair corrupted at least one Imperial Guard regiment standing watch on Aurelia. They became his worshipping servants. In one scenario, the newly re-tasked Lord Eliphas slaughtered the heretical Guardsmen and then recruited Ulkair into his forces. Ulkair was pleased at the prospect.