Even before the Stygian Wars Sarwen the sorcerer was a dark legend amongst the ranks of the Alpha Legion of the 7th Grand Hydra company. Originally an apprentice to Vilkor, Sarwen showed enormous potential. He gained more reputation as he led numerous raids throughout the long war and his talents continued to develop.
After a time the 7th Hydra came to the aid of a sorcerer of the Thousand Sons warband named Kopek. In exchange for their aid Lord Magwar arranged a five year apprenticeship for Sarwen under Kopek. While some questioned the value of the trade at the time it would prove to be a most beneficial deal for the Alpha Legion.
Sarwen already an adept summoner earned the respect and trust of Kopek loyally serving and learning from him. Kopek expanded the young psychers talents of biomancy and taught him to grow stronger with the death of others, even to use death to heal wounds. The dark arts of summoning where further expanded upon enabling Sarwen to command demonic tides of destruction unleashed with a word. Finally Sarwen was taught a little of the old lore of the Thousand Sons. He was taught to create his own tutelaries, some to serve as guardians and others as familiars. He was even shown how to leech life from an enemy and use it to enhance the power of his tutlary.
Sarwen returned to the 7th Hydra company of the Alpha Legion and shared much of his lessons with his fellow psychers. He and Vilkor quickly became rivals however with only Lord Magwar keeping peace between them. Sarwen then formed his own coven with Lord Magwar's permission.
When the Stygian Wars began Sarwen was given a chance to expand his power. He quickly became a hero to the Stygian Empire for his bloody victories and the honorary title of the Slaughter Sorcerer attached to his name. Death was his servant, he used it to strengthen his powers and himself often before unleashing the daemons of the warp upon reality. In time he was even given command of large militia units and brigades as was the case when Operation Scimitar was launched.