In the beginning...
The Black Wolves were formed by the Space Wolves who discovered their planet, Valaya, far up in the galactic north, an area which had previously been cut off from the rest of the galaxy by fierce warp storms.
On Valaya the Space Wolves found a race of hardy tribesmen, not unlike those on Fenris, who lived in large villages in Valaya's dense jungles. The Space Wolves were amazed at the raw ferocity of the Valayans and decided that they would be perfect to join the ranks of the Space Wolves. Unfortunately, the Valayans were as stubborn as they were fierce and refused to join.
Eventually a compromise was reached, the Valayans would have their own chapter, named the Black Wolves after the Valayans god of war, and some of the Space Wolves would stay on to train the new recruits in the ways of warfare, as well as providing them with the precious gene seed, without which they would be unable to become Space Marines.
Problem Gene Seed
It was soon found that the Black Wolves were even more ferocious than the Space Wolves, but that was not all. Every Valayan had in them a protein that effected the working of their gene seed. The protein made the gene seed give out unusual chenical signals to the rest of the Marine's body causing the mass production of numerous hormones and a sharp increase in the senses. This process often sent the Marine mad and it took many years before the Wolf Priests were able to slow the reaction time until it took a number of years before the protein began to react.
Eventually the reaction time was slowed down so much that many Marines died before the protein was able to take effect. Unfortunately, some Marine's proteins reacted faster than others creating a mass of half-mad Marines that were unable to complete even the simpilist of tasks. While the higher members of the chapter were deciding what to do with these Marines an amazing event took place, one by one the Marines left their insane state and appeared to behave normally. The Wolf Priests ran numerous tests on the Marines and found that although they were perfectly sane, they were also more agile and powerful than before, and they also thought thought they were wolves!
The Executioners
The changed Marines did not fully believe they were wolves but acted as if they were part of a large pack. They still donned their power armour and carried bolt pistols like the other Space Marines but also howled across the comm-net and exhibited other strange behaviour. The most unusual of which was the tendancy to eat the bodies of their fallen enemies, no matter what race they were fighting.
The Black Wolves were quick to capatilise on this by sending the Marines into battle in packs, called the Executioners by the Black Wolves after the way they execute their enemies.
The Ulfwereners
The Executioners aren't the only the unusual troops though. From the densest Valayan jungle came the Ulfwereners, a tribe of warriors with an unique ability. They are all able to turn themselves into a large man-wolf creature called the Wulf by the Valayans. The Wolf Priests have yet to find out what allows the Ulfwereners to make this change. The Ulfwereners were quickly accepted into the Black Wolves chapter, much to the despair of their enemies.
Powerful enemy
The Black Wolves are often looked on as savages by many Imperial commanders and are not as popular as the other Space Marine chapters. But it is this savagry and mistrust that makes then such a potent fighting force. They are powerful enemies in close combat and spend most of their time fighting the enemy by themselves.
Their natural ferocity has made them the bane of many enemies of the Imperium, especially the Orks, who have fought the Black Wolves on numerous occasions. The Black Wolves have held a special hatred towards the Orks ever since the Orks destroyed a number of tribal villages on Valaya, the Black Wolves home planet. The Orks attacked with the force of a tidal wave, albeit a green one, raising many villages to the ground before being surrounded by a very large, and pissed off Black Wolves army.