Orks are amongst the most violent and aggressive species known to exist in the fictional universe of Warhammer 40,000, to the point that Ork culture is almost exclusively geared towards war.
they are greedy, dumb and unbelievably destructive and care only for fighting and conquest, though in truth conquest is not as big a deal to Orks as the thrill of combat. It is usual for Orks to gather into a spectacle of bloodlust known as a "WAAAGH!", which is a massive mix of mass migration, genocidal war, full-scale pillage and religious conflict (as orks try to please their twin gods, Gork and Mork). Once one of these frenzies has started few - if any - foes caught in the storm of violence that ensues live to tell the tale.
The Orks are also one of the main threats to human domination and survival in Warhammer 40,000 - rivalled by the Chaos, Tyranids, and Necron (there are infinite other minor alien species but all are said to pale in comparison to these threats).