WAAAAAAAAAGGGGGGHHHHHH!!!!!!

The Orks, also called Greenskins, are a savage, warlike, green-skinned race of humanoids who are spread all across the galaxy. They are seen by their enemies (pretty much everyone else in the galaxy) as savage, warlike, and crude, but they are the most successful species in the whole galaxy, outnumbering possibly every other intelligent race, even Mankind (with the very plausible exception of the Tyranids, who are split between thousands of subspecies genetically engineered for specific purposes). However, this massive population of Orks is split into hundreds of tiny empires, often warring between themselves. It has been speculated that, were the Orks ever to unite as a single racial entity, they would undoubtedly crush any opposition that would stand against this sheer tsunami of green muscle. Luckily, the Orks enjoy killing each other just as much as they savour shedding the blood of the galaxy's other peoples.
First and foremost amongst all of the Orkoid instincts is the literal need for an Ork to wage war. Orks need war just as a human or Eldar needs food and water and over the long millennia of their existence the Greenskins have become very, very good at it. Due to their inherently aggressive nature, Orks constantly fight amongst themselves to prove who is the strongest, sharpening their in-born warrior skills and weeding out the weak, though this process usually poses little threat to the larger galaxy. However, Ork populations can reach a form of critical mass that can unleash a full-scale interstellar migration of Greenskins. This violent migration and the planetary assaults that result from it is what Imperial savants refer to as a WAAAGH!, a crusade of pure aggression that crashes through multiple star systems in an absolute orgy of fury and violence.

GREEN IZ DA BEST!!!!