Inar Satarael was an Archmagos Prime of the Adeptus Mechanicus. One of the most infamous Magos Prime of the Great Crusade, many labeled him mad. His record began on the ravaged Forge World of Incaladion where he battled outside invaders. In fighting off one savage attack after another he rose in power and status among his kind, finally gaining a seat on the world's ruling council of Magos. However later in battle against a rare Xenos race known as the Carnoplasm, his flesh was liquefied and drunk from his body.
Astonishingly enough, Satarael lived through the attack. His consciousness remaining in his body's damaged cogitator units. He used Servitors to rebuild his damage organics using stolen biomass. After managing to restore his cerebral cortex he was reborn but it was whispered he was no longer sane but rather a malevolent savant-warrior obsessed with power and immortality.
When the Great Crusade came, the rulers of Incaladion were more than happy to grant Satarael his own independent command. His forces served with brutal distinction for decades alongside Expeditionary Fleets and when the Horus Heresy broke out he joined the traitorous forces of Warmaster Horus.