|This page contains spoilers for:||Horus Rising (Novel)|
|This page contains spoilers for:||Know No Fear (Novel)|
|This page contains spoilers for:||Fear to Tread (Novel)|
In the local legends of Sixty-Three-Nineteen, the Whisperhead Mountains range was an area where the barriers between reality and the spirit world were most permeable. According to their mythic history, one of the first "Emperors" of the planet had combated and restrained a very malignant spirit, called Samus, in the area. Over time, that spirit had come to be seen as the local equivalent of "the Devil," who was nevertheless prayed to by some of the rebellious natives in the face of the Imperium's annexation of the world.
Several fanes and shrines were dedicated to Samus throughout the Whisperhead region, the majority of them in the caverns of the highest peak. During the Battle of the Whisperhead Mountains, the Imperial forces destroyed these as they advanced through the territory. While the Imperium later conjectured that Samus was somehow deliberately unleashed upon them, it is also possible that these fanes were part of the restraint placed upon Samus (if the old legend is believed) as his attack came soon after around thirty of them were destroyed.
Samus possessed the body of Sergeant Xavyer Jubal of the Luna Wolves Space Marine Legion. In this form, Samus was able to eliminate over a dozen Marines before being defeated. He also killed several remembrancers accompanying the Wolves' deployment.
Samus was defeated when Captain Garviel Loken and Sergeant Nero Vipus fired over ninety bolt rounds into his body, bursting it apart beyond capacity to operate, and then incinerated the remains with a flamer. It is probable that Samus's spirt was banished back to the freedom of the Warp by this action, no longer restrained to the one location.
The entire "Samus incident" was hushed up by order of the Warmaster Horus, to hide both the knowledge that an Astartes had turned on his fellows, and that it was possible for malignant warp-entities to corrupt them.
Samus is also mentioned in another novel in the Horus Heresy series, Fear to Tread by a Bloodthirster addressing Horus via a demonic means of communication. He says "Samus sends his regards. And now the game begins." 
In addition to his ability to possess mortals, which made the bodies in question look significantly aged, Samus had enhanced strength, enough to crack open power armour with a directed strike. Samus was also able to interrupt and even wash out vox-channels of the Imperial forces with an unnerving, repeated chant:
"Samus. That's the only name you'll hear. Samus. It means the end and the death. Samus. I am Samus. Samus is all around you. Samus is the man beside you. Samus will gnaw on your bones. Look out! Samus is here."
This was thought to be rebel propaganda broadcast over the communications network, even though there were reports of individuals without personal vox-sets hearing the voice of Samus as ghostly whispers.
While the death of his mortal host incapacitated him for a time, he was eventually able to animate and change the body, taking on a gross, distorted aspect that featured a dog-like head, hunched posture and long claws.
- 1: Horus Rising (Novel) by Dan Abnett
- 2: Know No Fear (Novel) by Dan Abnett, Target/Engagement, Chapter Ten, pg. 319
- 3: Fear to Tread (Novel) by James Swallow, Chapter Nine, pg. 260