The former Chief Apothecary of the Imperial Uhlans, Marcus Blasius along with the rest of the chapter's Apothecarion were stolen from their vessels during a hazardous warp journey in which the chapter were lost in the warp for two decades. They were corrupted by the Plague God, Nurgle, into a vicious warband of plague spreaders, terrorizing citizens of the Imperium for the next few millennium.
Being a former Apothecary has given Blasius an intimate knowledge of disease, allowing him frightening efficiency in spreading the Plague God's will, using a special Bolter blessed by Nurgle himself called Pox Spreader. The weapon infects it's victims with various different poxes and diseases which eventually decomposes the body into a festering mass of puss and boils, which in turn can be used as more ammunition for the weapon. Using the weapon with terrifying efficiency, he has spread disease to millions of individuals, all in the name of the Pox God.