Tarkh'ax is a Lord of Change, a Greater Daemon of Tzeentch. Tarkh'ax manufactured a conflict between the Imperium and the Tau on the world of Dolumar IV after corrupting the Imperial Governor of that world where it had been imprisoned by the Eldar Songweave for more than 10,000 standard years.
Tarkh'ax is a Lord of Change who was trapped during the 31st Millennium by Eldar Farseers on the Desert World of Dolumar IV. They were able to achieve this victory through the use of a powerful psychic incantation known as the "Songweave". These powerful enchantments sealed the Greater Daemon and his Word Bearers Chaos Space Marine followers within an abandoned section of the Webway. Ten millennia later, Tarkh'ax plotted his escape from the accursed Eldar trap, manipulating the planet's Imperial Governor Meyloch Severus to release him from his dimensional prison.
The Greater Daemon orchestrated a war which soon erupted between the Imperium of Man and the upstart xenos race known as the Tau, after the Ethereal Aun'El'Ko'vash was kidnapped by Captain Ardias and the Astartes of the 3rd Company of Ultramarines, under the orders of Governor Severus. During the conflict, Severus performed a Chaotic incantation, summoning forth Chaos Space Marines of the Word Bearers Traitor Legion onto the orbiting Imperial Battleship. The boarding force of Traitor Marines was eventually repelled, and the Tau launched a counter-boarding action of their own, but the ship was eventually destroyed by the Word Bearers.
In the meantime, Governor Severus took cover within his personal fortress to wait out the inevitable carnage. The Governor was later discovered and killed by the vengeful Fire Warrior Shas'la T'au Kais, a willing blood sacrifice to release his true master, Tarkh'ax, from his imprisonment. Unbeknownst to the young Tau, he too, had been an unwilling pawn of the Lord of Change. Having sacrificed himself at the appointed time, at sundown, the Daemon Lord was able to possess Severus' corpse as his Daemonhost, revealing himself in all his malefic glory. The Lord of Change then unleashed hell on earth, summoning forth a tide of warping energy upon his foes. Reports on the outcome of the final confrontation with the Greater Daemon vary, and are often contradictory. Some claim that the Fire Warrior Kais was able to defeat the daemon single-handedly, while others state that he was helped by both the Ultramarines Captain Ardias and a Tau Crisis Battlesuit team led by Kais' commander, El'Lusha. With his defeat at the hands of the mortal races, Tarkh'ax's spirit was cast screaming back into the Warp.
- Fire Warrior (Novel) by Simon Spurrier
- Fire Warrior (Video Game)