Xarl was a member of the Night Lords and close friend to Talos Valcoran, also known as the "Soul Hunter". Xarl and Talos grew up on Nostramo together as children and were members of the same street gang, fighting for survival on the unforgiving streets of the Night Lords homeworld. Later, both were inducted into the Legion and served alongside each other in First Claw, 10th Company, in the Great Crusade and Horus Heresy. Xarl continued to fight alongside Talos in his power struggle with Vandred Anrathi, during the Fall of Vilamus, and later during Talos' return to Tsagualsa, the place where millennia before their Primarch had been slain. After terrorizing the planet's populace, retribution from the Imperium came in the form of the Genesis Chapter of Space Marines. Xarl and Cyrion found themselves in a desperate battle against the Company Champion, Tolemion. Taking savage wounds from the loyalist Space Marine's Thunder Hammer, Xarl managed to finally slay the Champion with his Power Sword. However, the wounds that he had taken in the struggle were too much for even an Astartes to endure, and shortly after Talos' arrival to the scene he collapsed into the Soul Hunter's arms and died. The act enraged Talos, who went on to pursue and destroy the Genesis Chapters Strike Cruiser.