If you want to dive deep into Plague Marines lore, then this video is a must-watch! Join me as I explore the dark and twisted world of these infamous warriors in my very first 40k short upload. #warhammer40k #deathguard #chaosspacemarines #lore #explained #warhammercommunity
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They some happy boys.
I should add, they didn't willingly turn to chaos. Mortarian hated chaos and anything warp touched. It was Typhon that forced this to happen. He was Mortarians close friend from the plague world and a powerful Psyker which Mortarian did not like and always told him to supress.
Basically, Mortarian only joined the Traitors because he saw it as an opportunity to kill all the Imperial Psykers (And then likely would have turned on his traitor brothers to kill theirs too). Typhon saw this as a opportunity and tried to convince Mortarian to turn Chaos which he refused.
So when the siege of Terra began and the Deathguard were summoned to join the fray – Typhon told Mortarian their Navigators were still loyal and would betray them – and he offered his own to Mortarion.
Turns out it was all a lie, with the Navigators dead they became trapped in the warp and fully exposed to the entities therein.
Nurgle hand crafted a special plague designed specifically for the hardy deathguard to make them suffer in great pain for eternity – and Nurgule in his true form manifested before Mortarian and told him the only way to end the suffering of his sons would be to submit. Out of love of his sons Mortarian reluctantly submitted and Nurgle warped them into what they are now.
For handing him the Deathguard, Typhon was named Herald of the Plague God and became Typhus.