We are all tyrants. Do not fool yourself. We were bred for nothing else.Mortarion the Reaper.
Mortarion is a quixotic figure. Black Library fiction is at its best when investigating the discrepancies that have been thrown up throughout the years, rather than try to heal them.
Mortarion reviles the Warp and any magic-user. He has a turbulent past with the Witch things that fostered him in his infancy on Barbarus. And yet he a flagrant user of the arts.
He is a hypocrite.
He is an addict.
The fall of the Deathguard is one of those treasured parts of the lore. We all have our own conception of the Devil’s bargain struck to save his legion. My own head cannon has his fleet becalmed in the Warp after the pursuit of the White Scars into the deeper etheric currents of the warp.
Typhus becomes the voice of Nurgle, Death’s spectre walking abroad The Endurance as Mortarion, Mortarion’s dealings with the Warp, his albatross around his neck. As a Primarch, he is functionally immortal and must endure the slow erosion of his fleet, then himself, until he becomes a will without a body, a mind without a voice. The dance of stars and galaxies play before him, a witness to the entropy of the Universe as the Ouroboros takes it’s last bite.
The Universe does not care for the struggles of Horus, or the Emperor, or the clash between Chaos and Order. It does not share our sorrows, as the Universe does not see us at all.