Tarkh'ax was a Lord of Change that was trapped by the Eldar in M31 on the desert planet of Dolumar IV, by the means of a psychic incantation known as the Songweave. This held Tarkh'ax and his army of Word Bearers within a section of the Webway, which was then sealed off. it was only by the actions of the planet's Governor, Severus, (under, as it transpired, the subtle control of Tarkh'ax) that he, and his army were released. It took an orchestrated war between the Imperium and the Tau and chaotic incantations to release the army, and the blood sacrifice of Severus himself at the precise time of sundown (this action carried out by Shas'la T'au Kais, another pawn of the Daemon) to summon Tarkh'ax himself.
During his brief foray into the Materium he recieved blessings from each of the Chaos Gods before losing them again in conflict with Kais, Shas'el T'au Lusha and Captain Ardias, before being destroyed entirely by Lusha and a squad of Battlesuits.