Ka'jagga'nath the Unbound, known as the Lord of the Bloodtide, is a Bloodthirster, a Greater Daemon of the Blood God Khorne who unleashed a murderous daemonic infection upon the people of the Imperial world of Van Horne. Little is known of this powerful Daemon Lord other than his ability to summon forth a great corrupting wave known as the Bloodtide. What the Bloodtide truly consists of is as unfathomable as the goals of Ka'jagga'nath himself, and some say that it is blood given purpose or perhaps pure unbridled Warp energy. Others even claim it to be a machine or weapon of ancient and unholy design. The truth may never be known, but some dedicated servants of Khorne have been able to obtain a fraction of this power, conjuring some dark facsimile of the fabled Bloodtide to wash away those that stand in the path of Khorne's plans.
In the year 876.M41, within the Basilica of St. Mariel on the Imperial world of Van Horne, an ancient prison was accidentally damaged during renovations. A forgotten stasis-reliquary within the basilica contained the spirit of the infamous Bloodthirster Ka'jagga'nath, the Lord of the Bloodtide. Breaking free of his imprisonment and possessing the body of one of the workers to serve as his Daemonhost, the Greater Daemon unleashed a tide of gore, which washed through the basilica, corrupting everything and everyone it touched. The Emperor's most virtuous servants were soon afflicted with the murderous gall-fever that rendered them into homicidal maniacs. They roamed the nearby streets to abduct hapless innocents and sacrifice them upon a desecrated altar of blood. In an orgy of destruction that lasted 8 days and nights, the ensuing carnage attracted more and more daemons through to Van Horne from the Warp as the local barrier between the Empyrean and realspace weakened. Within only a matter of days, the Bloodtide would have corrupted the entirety of the planet. On the morning of the ninth day, the Battle-Sisters of the Adepta Sororitas' Order of the Ebon Chalice assaulted the basilica, resulting in some of the Sisters being corrupted by the malefic Bloodtide. The survivors endured valiantly but were soon slaughtered by a horde of Bloodletters that had taken up positions atop the basilica's walls. The Bloodtide only abated with the arrival of the Grey Knights' 4th Brotherhood on Van Horne.
Turning their blades upon the surviving Battle-Sisters, the Grey Knights sated their blades in their innocent blood, effectively turning their weapons and armour into talismans of purity. The Grey Knights were then shielded from spiritual infection by the goreflood of the Bloodtide and were able to make their way into the heart of the cursed basilica. Led by a trio of their Chapter's formidable Librarians, who enunciate the cants of cleansing to repel the Bloodtide wherever they tread, the Grey Knights found the Greater Daemon at the centre of the building's rotten heart. Ka'jagga'nath was only defeated by the valiant sacrifice of the 4th Brotherhood's Champion, Ordan. Before the Bloodthirster's spirit could escape its broken body, the Grey Knights cast its foul soul back into the Empyrean, which also banished the Bloodtide and the summoned daemons back with it as part of a powerful psychic backwash.
- Black Crusade: The Tome of Blood (RPG), pg. 60
- Codex: Grey Knights (5th Edition), pg. 15