From Lexicanum

Space Wolf legend states that the group that came to be known as Thirteenth Company was sent by Leman Russ to pursue the survivors of the Thousand Sons, after a failed attempt to eliminate them at their homeworld of Prospero⁴. The members of the 13th company swore to hunt their foes down until every last one of the cursed marines was slain, no matter how long it took, nor where the traitors fled. It has been said that the 13th Company currently is being led in their mission by none other than Leman Russ himself. This is, of course, like most of the information pertaining to the 13th Company, impossible to verify.¹ They vanished from Imperial records, and their loss is honoured by a black stone in the Grand Annulus (the record of Space Wolf Great Companies).

Magnus through his arts, scryed the future, and seeing the treachery of Horus, used his sorcerous arts to send a message to his liege. The Emperor, however, did not believe that his son Horus who was much beloved could betray him, and instead sent Leman Russ, Primarch of the Space Wolves to bring the Thousand Sons to account of their actions, now suspected of attempting to spread discord and sedition between the Emperor and his sons. Russ took his Legion, and with all the Great Companies of the Space Wolves, fell upon the World of the Thousand Sons, Prospero, with the vengeful force of a mighty shower of comets.

The Space Wolves attacked the Thousand Sons largely because of Horus, who tricked Leman Russ into believing that Magnus' crime far outweighed that of simple meddling with sorcery, and on the field of battle, at its forefront was the Thirteenth company who with incredible ferocity fell upon the Thousand Sons. These could not stand against the righteous force of the Space Wolves, and inch by inch grudgingly gave ground, until they were surrounded in their own Fortress Monastery, and determined to stand to the last man.

Meanwhile Magnus, Giant Cyclops lord of the Thousand sons knelt in his tower and wept as his sons were ripped away from him. In his anger and sorrow he called to all who would listen and one voice answered. Tzeentch the Manipulator, at the moment Magnus gave his soul Tzeentch granted the traitorous Mutant full mastery of the vagaries of sorcery, and Magnus with his new found power took the battle back to the Wolves of Russ.

Appearing amongst the lines of the Space Wolves, Magnus was unstoppable, and even the Feral brotherhood of the Wulfen was unable to stand before him. All fell before him until the great Primarch of the Space Wolves, Leman Russ, advanced upon his Brother. The battle between these two titans was fierce, and would fill several tomes. Magnus managed to pierce the secondary heart of Leman Russ and gouged a mighty rend in his flank but Magnus's forte was not in battle, but in wit and intellect, and after two days and two nights of combat Russ took the battered body of Magnus, and raising him to the storm wracked skies, brought him down upon his knee.

With a mighty crack, Russ broke the back of his foe, and the heart of his enemy. Magnus sunk to the floor, and as Russ raised his fiery sword Mjalnar to strike his enemy's heart, Magnus whispered a single word of Power and sunk into the earth's dark embrace.

As Leman Russ howled his fury to the packs of the Space Wolves, the sorcerous-librarians of the Thousand Sons opened a vast maelstrom of energy, through which their forces fled. The Wolfkin, the Thirteenth Company of the Space Wolves, in a response to their Primarch's feral rage, gave tongue to the chase and followed their foes into the very eye of the Warp. With a blinding flash, the swirling maelstrom of energy collapsed and the Thirteenth Company, passed from this plane and from Imperial history.'"

Their reappearance at the beginning of Abaddon the Despoiler’s Thirteenth Black Crusade has brought them back into the spotlight. They appear to still be in pursuit of the goal Leman Russ set for them, and it was believed that Leman Russ himself was their leader, although this was never proven.

The Thirteenth Company's organization departs heavily from Space Wolf norms, due to the lack of reinforcements and 'fresh blood' supplying the Company, the inability to train members in specialist roles, the lack of heavy equipment, and the effect of having to exist within the Eye of Terror for ten thousand years.

The core of a 13th Company warband are the Grey Slayers. Similar to Grey Hunters but far beyond them in skill, they fulfil the same roles in battle.

Because of the impossibility of recruiting new brethren, there are no Blood Claws in the 13th Company. Each and every Blood Claw has long since advanced to a higher stage. The Company's assault specialists are the Storm Claws. They are equally experienced, but still more hot-headed and aggressive than the Grey Slayers.

The key to the 13th Company's movement through the Warp are the Rune Priests. Because the Eye of Terror has unlocked hidden psychic powers in many recruits, the Company has no shortage of these highly gifted individuals.

The Wulfen are the most drastic departure from a normal Space Wolf. The Space Marines who mutate into Wulfen bear resemblance to werewolves in the same way as Blood Angels suffering the Red Thirst resemble vampires. Any marine to suffer as a Wulfen becomes a half man, half wolf creature with a feral mind. The mutation normally manifests itself in the neophyte stage and Space Wolves must spend time in their training in a scenario designed to out those who have become Wulfen.

Though normal Space Wolves sometimes use individual Wulfen in battle, the 13th Company use entire packs. Each and every member of the 13th Company carries the Curse, and it manifests itself in the Space Wolves at different times. Thus even the Wulfen packs do not stay the same. It has manifested itself so strongly and so late because it reacts to the influence of Chaos; because of this side of their nature acting as a kind of spiritual defence mechanism, Space Wolves are exceptionally resistant to the malign influence of Chaos. It is believed that the 13th Company have only been able to survive living as loyalist marines in the Eye of terror so long precisely because of this trait.

The 13th company was introduced into play in the Eye of Terror Campaign. The 13th Company cannot be used with the normal Wolves, but this is only a balance issue. The story "Engage the Enemy" shows the Space Wolves going so far as to lie to the Imperial Guard to protect the 13th Company.

They are said to be lead by a Wolf Priest nicknamed the Sternhammer who can control the Wulfen Guard Packs but only barely.

Somehow, the hardy Sons of Russ survived their journey through the Eye, and have emerged, long after they should have perished, in pursuit of the foul Despoiler Abaddon.¹ The powers of the Warp are said to be able to affect time itself, and such things have been known to happen before, as starships are lost in the warp for centuries, only to reappear with the crew barely aged a day.²

One other thing that sets the warriors of the 13th Company apart from the rest of their Space Wolves brethren is the large percentage of warriors who have succumbed to the animal nature that is part of the genetic legacy of their Primarch: the Mark of the Wulfen. This genetic mutation causes their canine nature to manifest itself more fully and, amongst other things, thick hair to grow over all the body and claws to sprout from the hands. These warriors gather together in units and surrender themselves to their animalistic nature, rushing headlong at their foes, eager to use their sharp claws and teeth in close combat. Whether the increased percentage of 13th Company Marines who have succumbed to the Mark of the Wulfen is a result of their exposure to Eye of Terror, or whether it existed before and their increased percentage in the Company is simply due to the fact that their increased stamina and strength has allowed more of them to survive than their brethren is, of course, unknown. ³

The 13th Company is also distinguished by maintaining the dark gray Pre-Heresy colour scheme of the Space Wolves on what little remains of their original equipment. Much of their armor and weaponry has been replaced with material scavenged from their fallen Chaos foes. Not surprisingly, their Company has almost no heavy equipment such as tanks, terminators or dreadnoughts. ³

Sources

• ¹ Games Workshop Codex: Eye of Terror
• ² Lexicanum: The Warp
• ³ Games Wokshop Online: 13th Company Army List
• ⁴ Wolf's Honour by Lee Lightner