Kyriss, known also as Kyriss the Perverse, was a Keeper of Secrets, a Greater Daemon of Slaanesh, who was active during the Horus Heresy in the early years of the 31st Millennium. Alongside the infamous Bloodthirster Ka'Bandha, a Greater Daemon of the Blood God Khorne, Kyriss served as one of two daemon overlords or "generals" who helped orchestrate the Signus Campaign, in a coordinated effort to lure the Blood Angels Space Marine Legion to the Signus Sector and corrupt them to the worship of the Ruinous Powers.
This was primarily done to draw the IX Legion away from the Segmentum Solar so that they could not interfere with the Warmaster Horus' plans to launch his final offensive on Terra, the Imperial Throneworld. Unknown to Kyriss, however, both the Warmaster and Ka'Bandha intended to use him as a sacrifice in order to drive the angelic Primarch Sanguinius into the depths of a rage that would pull both himself and his Legion into the worship of the Blood God.
After a climatic battle with Ka'Bandha, in which the Bloodthirster was forced back into the Immaterium, Kyriss schemed against Sanguinius and attempted to tempt the Primarch with a devil's bargain -- he would spare the Angel's sons from both the Red Thirst and the Black Rage if Sanguinius was willing to sacrifice himself, to take the incessant rage within him and step into the Realm of Chaos. But Kyriss' plans were foiled when the Blood Angels Apothecary Meros volunteered himself in his gene-sire's stead, becoming the daemonic entity known as the Red Angel in the process. Enraged at the loss of one of his sons, and to honour Meros' noble sacrifice, Sanguinius sliced Kyriss' head from his body, sending the Greater Daemon screaming back into the Warp to face the displeasure of his dark master.
- Fear to Tread (Novel) by James Swallow