As you are all no doubt aware, for generations the most consistent threat to our humble corner of the Imperium is the Orks. Spread as they are across the entire sector, in numbers rivaling that of humanity, these savage creatures know only war. From sporadic, localised raids and battles to sweeping invasions that have razed planets and killed or enslaved millions of humans, the Orks have been fighting against us on hundreds of worlds and throughout the depths of open space, especially around the Denebian asteroid belt. I have included a short quote from Harda's Xenoptium to remind you all just what we face here.
"Orks are naturally built for bloodshed. Although usually stooped, an Ork stretched to its full height towers over a man, and Ork leaders, older and subjected to years of violence, are massive creatures able to crush a man's head with a clawed fist. Orks have a thick leathery skin, varying from sickening green to almost black in colour, which is extremely resilient to damage. In fact, their whole physiology makes them very difficult to injure and quick to heal. Rows of fangs, up to a finger's length, jut from their bucket jaw, and slab-like muscles move under their rough, warty skin. Their red eyes and permanent snarls give them an angry, bestial look that is altogether appropriate for their temperament. In combat they are vicious and pitiless, with a total disregard for life-theirs or their enemy's. They show little tactical or strategic sophistication, but their bloodthirsty nature, mixed with a degree of savage instinct and low cunning, make them fearsome adversaries."
My recommendation is that we dispose of these vermin as quickly as we can. If allowed to increase their numbers unchecked they will cause us untold trouble in the Sector.
-as quoted by Xenobiologist Fremant, Palladium Colony, from the Warhammer 40,000 rule book
Orks can be extremely entertaining to play with or against. Even though they are gunned down in large numbers, they still press on and sometimes even pull off a victory. Also, in second edition, they had a tendency to do some pretty whacky stuff.