Mortarion

Origin & Rediscovery

Barbarus was a poisoned world. Its lowlands sat in a thick warm fog of toxic gases; its highlands climbed past lethal altitude into thin air no baseline human had ever survived. The Overlords — psyker-sorcerers who had bred themselves over generations to endure the upper-altitude poisons — ruled the planet from peak-fortresses, descending occasionally to collect tribute from the lowland tribes that scraped survival out of the lower fog.

The infant pod fell into the lowlands. One of the Overlords, more curious than predatory, recovered the child and carried him to a peak-fortress out of an instinct he never bothered to examine. He named the boy Mortarion and raised him as a curiosity. He taught him, in time, the sorcery that the Overlords used to dominate the lowlands. Mortarion learned it carefully, hated every minute of the learning, and waited.

The day his body could finally endure the altitude long enough to climb Barbarus's tallest peak alone, he climbed it. He killed his foster-father. He led the lowlanders in a generational war against every Overlord left on the planet. The Emperor arrived in the middle of that war. The two of them argued — about poison-tolerance and gene-craft and the relative merits of unaided strength — until the Emperor agreed to finish the war for Mortarion's sake. Mortarion accepted the Emperor's authority with conditions. He never quite forgave Him for finishing what Mortarion had wanted to finish alone.

The Hatred

Mortarion hated psykers. The Overlords had been psykers; the sorcery he had learned and unlearned had been their gift and their humiliation; he transferred his Barbarus-grown contempt onto every warp-touched mind he met afterwards. He refused to recruit Librarians into the Death Guard. He argued with the Emperor about the psyker corps and lost the argument every time it was raised.

The Death Guard he built were a slow-grinding infantry of toxic survivors — the Imperium's specialists in fighting under poisonous conditions where cleaner regiments would simply die. Their armour was sealed against atmospheres that would have killed other Astartes. Their physiology was tuned by Mortarion personally for endurance over speed. They were not the fastest Legion. They were the Legion that arrived eventually no matter what the terrain did to slow them.

There is no enemy I cannot outlast.

— Attributed to Mortarion

The Destroyer Plague

When Horus turned, Mortarion turned with him. Whether out of solidarity, ideological grievance, or simple long-festering hatred of Imperial bureaucracy, he committed. Then, in the warp on the way to a planned Heresy engagement, the Destroyer Plague struck his fleet — a virus that should not have been there, that affected even Astartes physiology, that was killing his Legion in tens of thousands across compartments that should have been sealed.

What Mortarion did not know — and would not learn until centuries later — was that the plague had been engineered by Typhus, his own First Captain, who had been a secret Nurgle-cultist throughout the Crusade and had calculated the crisis precisely. The bargain Mortarion was about to accept had been arranged before he understood it was being offered.

In desperation he pledged the dying Death Guard to Nurgle. The plague stopped. The Legion did not die. They simply became something else — eternal, rotting, immune to pain. The man who had spent his life refusing sorcery had become, by another name, the most sorcerous Astartes commander alive.

The Heresy

The Death Guard fought through the Heresy as Nurgle's instruments. Their tactics did not change; they had always ground armies down. Now they were unkillable while doing it. Mortarion accepted this in public and chewed on it in private. He was, by his own standard, no longer himself — and his Legion no longer his — but the alternative had been to watch them all die in the warp, and that alternative had been arranged for him before he could refuse it.

At the close of the Heresy he ascended formally to daemonhood. He now rules the Plague Planet in the Eye of Terror. He has not, in any documented appearance since, smiled.

The Plague Wars

In the Era Indomitus Mortarion invaded Ultramar with the full Death Guard. The Plague Wars saw him face Guilliman at the Battle of Iax — the only confirmed primarch-on-primarch duel of the modern era. Guilliman won. Mortarion fled wounded.

The war is ongoing. Mortarion has returned to Ultramar several times since, each time at smaller scale, each time leaving additional worlds blighted. By his theology — to the extent he has one — the matter between him and his brother remains unsettled. By Guilliman's assessment, it remains very settled and Mortarion is simply refusing to accept the result.

My brother's blade is sharper than I remembered. I have time. He does not.

— Mortarion, attributed post-Iax

Legacy

The Death Guard and Plague Marines are the most thematically consistent Chaos Legion — every member is rot personified, every campaign a slow grinding plague-vector. They are Nurgle's favoured sons and, in the order their primarch would have preferred to be remembered, Mortarion's.

Typhus operates somewhat independently with his Plague Fleet. Mortarion has never publicly confronted him about the Heresy-era betrayal. The two of them no longer speak. The Legion treats this as normal.