The Ursarax were first designed by Magos Explorator Enabrin Falkan as a heavy, rapid-moving close combat unit. Using a fusion of existing technologies sacred to the Mechanicum, materials and patterns taken from the Thallax of the Ordo Reductor, and the fruits of Falkan's own discovered, he created a monstrous killing engine.
Like the Thallax, they are Thralls rather than Servitors, selected from suitable human candidates for conversion so their living components retain a consciousness and dim recollection of their former selves. Neural anesthesia is automatically administered for the successful fulfillment of their orders, providing them with temporary relief from their tortured existence. After Falkan's mysterious disappearance, his warring acolytes dispersed to many different masters, taking the secret of the Ursarax with them.