While the exact origin of the Orks is unknown, the limited information available indicates that they were genetically engineered as a sort of biological weapon by an extinct race the Orks call the "Brain Boyz". Who the Brain Boyz were and why they died out isn't clear, although there is speculation that they lost control of their own creations. Orks have been a problem for humanity for over ten thousand years.
The standard Ork is a large, heavily built, green-skinned humanoid with large tusks. They range from human-sized to up to six meters tall, although this fact is distorted by the fact that Orks stand hunched over. Orks are optimized for combat, being considerably stronger than humans of similar size, able to survive injuries that would easily kill a human, and able to quickly recover from nearly any wound that doesn't kill them outright. Like sharks, Orks constantly lose teeth and grow new ones, and also constantly grow larger and stronger, especially after recovering from injuries. Intellectually, the standard Ork lacks much in comparison with a human and is far more aggressive, being geared to revel in violence and battle.
Orkish technology is designed, created, and maintained by specialized "mekboyz", who are born with a highly developed -- if instinctual and subconscious -- understanding of machinery, science, and technology. Orkish equipment is typically rather simple but extremely rugged and robust and is often supplemented with captured equipment from other species. Orks even generate a passive psionic field that helps keep their ramshackle machines working. In addition to Mekboyz, there exist various other specialized subtypes of Ork with instinctive sets of knowledge such as "Mad Dokz" (medics and doctors in Orkish society, notable for intense mental instability) as well as groups of Orks which develop various manias, such being consumed with a desire to travel as fast as possible (such Orks are known as Speed Freaks and collectively as the Cult of Speed) or the extensive customization of their weapons (Flash Gitz). A small minority of Orks have powerful but erratic psionic abilities; these are known as Weirdboyz.
Orks are closely associated with several other creatures, notably the smaller gretchins and a variety of non-intelligent creatures -- ranging from rat-sized scavengers to monstrous beasts -- known collectively as squigs. All of these species are fungus-based life forms that reproduce via spores. An adult Ork constantly produces and releases spores (especially during and immediately after death) that propagate the Orkoid ecology, starting with fungus, then squigs. As the Orkish ecosystem spreads, gretchins develop underground in potato-like wombs and eventually the process gives rise to fully grown and capable Orks. Orkish ecology is deeply problematic, as even if an Orkish attack on a planet is defeated, it is quite likely that feral Orks will establish themselves on the planet, making complete and permanent removal of Orks extremely difficult. Planets that Orks attempt to conquer will soon have ecosystems which provide food, supplies, ready sources of reinforcements, and slaves for labor for the orkish invaders.
Orks have an instinctive catalog of behavioral characteristics they consider "Orky" and "un-Orky". While the exact criteria of "Orkiness" varies from group to group, it is generic enough to give orks considerable resistance to foreign corruption from Chaos or Genestealer infiltration; the appearance of massively "un-Orky" behavior results in corrective action, such as using the deviants for target practice. Occasionally, non-Orks can prove themselves to be Orky through actions, although this is very rare.
Status in Orkish society is determined primarily by size, with bigger Orks holding higher status. Larger Orks hold the title of Nob and maintain their positions through blunt physical force. Size among Orks is generally linked to longevity, combat experience and ability at surviving, which means that this method of leadership selection is more effective than what humans would assume on first inspection. The largest Ork in an established group holds the title of Boss. In combat this hierarchy is evident, with larger Orks being armed with superior (and thoroughly customized) weapons and armor and commanding smaller counterparts armed with "choppas" (simple bladed weapons similar to cleavers and axes) and low-quality firearms. For doing grunt labor, Orks make use of gretchens as well as captured slaves of other races. Orks naturally lack in terms of discipline, although they generally have large numbers on their side and some orks are capable of operating with some degree of stealth. Orks use their teeth as currency amongst themselves, this generally means that every Ork has access to some income and that Orks will often get into fights because one Ork wants to remove the other Ork's teeth.
Certain naturally dispossessed groups of Orks such as Mekboyz and Mad Dokz and those with specific manias (such as speed freaks) naturally gravitate towards one another and form subgroups in Orkish society, although these are strictly subordinate in the main Orkish hierarchy.
Beyond simple groups or "mobz", various "klanz" of Orks exist, sharing common ideology and sometimes biology. Among the more notable Klanz are...
- Bad Moonz: Bad Moonz grow new teeth faster than other Orks, as such they are in general more wealthy and generally can buy better equipment. On the other side, this makes them targets for other orks who want to steal their teeth.
- Goffs: Goffs are large and aggressive even by Ork standards.
- Blood Axez: Blood Axez are "cunning gitz" notable for their interest in tactics and adaptation, such as adopting Human equipment and methods after long-term contact with the Imperium of Man, thus making them more disciplined on the battlefield. This has made some orks view them as un-orky.
- Snakebites: Snakebites are traditionalists that make less use of technology than other orks, as well as having a larger number of weirdboyz.
- Evil Sunz: Evil Sunz produce more than their fair share of vehicle-obsessed speed freaks.
Orks worship two gods known as Gork and Mork. They are discernible by the fact that one is stronger and one is smarter and meaner, although which is which depends on which ork you ask, and holy wars have been fought over the matter.
When Orkoid ecology is established via spores on a planet after a developed Orkish society has either moved on or been defeated, the Orks that first emerge are quite primitive, living in primarily simple hunter/gatherer groups until their numbers reach the point that their society can support Mekboyz and move onto the next stage of Orkish society. These are known as Feral Orks.
While the Orks are the most numerically vast force in Warhammer 40,000, they are far from united. Various Orkish factions are always fighting among themselves as much as they attack other races, and individual orks engage in constant bouts of violence for any number of reasons. The main risk they pose to the rest of the Galaxy is when an established population of Orks is collectively driven into a sort of mass migration known as a "WAAAGH!", in which large numbers of Orks gather and move out to new territory in search of a fight, picking up other groups of Orks. A significantly powerful WAAAGH! can devastate multiple star systems before it winds down, while simultaneously establishing Orkish presences on new worlds. It is possible that a massive WAAAGH! could emerge in which all of Orkdom could be united in a war against everyone else to over-run the entire galaxy, although such an event would take a particularly charismatic and capable Warboss to initiate it.