Ilya Ravallion was a member of the Departmento Munitorum bureaucrat during the Great Crusade and Horus Heresy. Born on Terra with a photographic memory, Ilya proved adept at all things logistical and was assigned as a Munitorum attache to Jaghatai Khan, Primarch of the White Scars. Ilya and Jaghatai grew somewhat close, often drinking wine and playing Go together. Ilya served alongside Jaghatai during the Chondax Campaign and helped see him through the crisis that erupted in the White Scars during the Heresy. Ilya proved instrumental in stopping the attempted coup by Horus loyalists led by Hasik Noyan-Khan, opening the docking bay of the Swordstorm for Shiban Khan's loyalist forces and then activating the teleportarion beacon that allowed Jaghatai to return to his fleet.
Four years later, Ilya's health had begun to deteriorate but she remained a vital adviser to the White Scars, who now considered her something of family. Ilya helped guide the Scars to the Dark Glass artifact due to her knowledge of the mysterious Navigator Pieter Achelieux, and during the Battle of Catallus urged that the Khan return to Terra instead of seeking to settle the score with Mortarion. Upon the sacrifice of Targutai Yesugei to activate the Dark Glass and open a portal into the Webway, Ilya was among the three he psychically sent his goodbyes to.