For Endgren the planet was stuck in its postion at the furthest point from the sun and didnt turn like it should one side of the planet had a low light but this light was blocked by another planet leaving part in a state of darkness as well. The Imperium wanted to evacuate the world fearing chaos incursion and wanted to establish a research facility. The Endgren's refused stating this world was their home and had been since before the age of the Imperium and they wouldn't leave. The Imperium let them in return for keeping their home on top of their tithe of mining which had been their priority over any other tithe they would give a 20% tithe of men for the Imperial Guard which at first was difficult but when the mines ran dry after nearly two thousand years of non-stop mining the dark planets only resource was its men.
By now in 750 M40 the planet and its inhabitants had changed, adapted to the cold and dark conditions as well as the toxic atmosphere from the years of mining and refining.
Endgren's are tall but slim with keen eyesight in dark enviroments their eyes are a constant milky violet their other senses have peaked as a result, when on worlds that arent dark they wear a advanced protective headgear that darkens the outside enviroment as well as being a constant rebreather that they must wear to survive for the air on most otherworlds are too pure for them.