Changes

[[Horus]] found Mortarion more difficult to bring to his cause than either [[Angron]] or [[Fulgrim]], and for a time it seemed the Warmaster may have failed to convince the Lord of the Death Guard. However, Horus at last found a chink in Mortarion's armorarmour; he was beginning to see the Emperor as having been corrupted with power and now was just another tyrant drunk with power. Indeed, Mortarion had become disgusted with what exactly the Emperor was, considering him a [[Warp]]-tainted "aberration" like his tyrant adopted father. Horus also used Mortarion's distrust of the Warp to his advantage, arguing that the Emperor had used the [[Warp]] in the creation of the Primarchs. Horus eventually used these doubts to bring Mortarion to his cause.{{Fn|6a}} Mortarion led his Legion in their betrayal of the Imperium at the [[Battle of Isstvan III]] and [[Drop Site Massacre]]. He later came to blows with [[Jaghatai Khan]] on [[Prospero]] after failing to convince him to join with them in rebellion. During the fight the two Primarchs were able to challenge the other, with the Great Khan proving faster and the Death Lord proving more durable.{{Fn|9}} Following the battle, Mortarion abandoned his pursuit of the White Scars and instead began a spiteful purge of the systems surrounding [[Prospero]]. During the purge, Mortarion encountered a [[Daemon]] possessing the body of a woman and was forced to kill it using his innate [[Psyker|psychic]] abilities despite it being against Imperial (and by this point, his very own) dogma. Realizing that the Emperor had lied to him about the [[Warp|Empyrean]], Mortarion vowed to master it.{{Fn|10}}