A Thrall Wizard, also spelled Thrall-wizard, is a normal human Sorcerer of Tzeentch who serves the Heretic Astartes of the Thousand Sons Traitor Legion and is drawn and trained from the mortal population of the Thousand Sons' homeworld of Sortiarius, the Planet of the Sorcerers.
Each tower contains dozens of Thrall Wizards who focus their power to rain magical destruction in the form of powerful bolts of energy down upon Tzeentch's foes from the towers' floating fortifications.
When the Thousand Sons first arrived on the Planet of the Sorcerers following the Battle of Prospero it had no native population to make suitable servants or new warriors. Over the many thousands of Terran years that the Heretic Astartes have lived on the Daemon World they have acquired such minions through raids throughout the galaxy.
This has led to the creation of a mortal servant class within the world's sorcerer towers. Some of these menials have occasionally broken free and fled into the hostile lands beyond the Thousand Sons' towers to join the various nomadic warbands led by Chaos Champions of the Thousand Sons and inevitably, those Champions who have risen from the ranks of the escaped mortals.
From these warbands arise the Champions of Chaos, and in particular Champions of Tzeentch, who are often recruited back to serve the Thousand Sons as more than mere menials. New captives are always taken by the Thousand Sons when they raid into realspace and so the mortal population of Sortiarius remains stable.
Individuals with psychic powers are highly prized and encouraged by the Thousand Sons. Mortals who possess such abilities may begin their careers bonded to a Thrall Wizard band in the service of a Thousand Sons Sorcerer. They are taught how to perform the simplest magical feats as part of the first step to becoming fully-fledged Tzeentchian wizards.
While apprenticed in this way they are placed under the direct command of a Thrall-Champion who may have arisen from the ranks of the ordinary Thrall Wizards themselves. In battle, these apprentices fight for their Thrall-Champion and use their psychic sorcery to support them.
In this way these apprentices begin a journey that may see them rise in time to become a Thrall-Champion in their own right, or even ascend to the immortal heights of a Daemon Prince of Tzeentch, though far more fail in their ambitions only to devolve into mewling Chaos Spawn.
- Realms of Chaos - The Lost and the Damned (1st Edition), pp. 268-270
- Chaos Space Marines Datasheet - Silver Tower of Tzeentch