Apocs are the last surviving remnants of the world's armies after an apocalyptic Event has left the planet as they know it completely shattered. Designed long before this world-shattering event, but with it in mind, Apocs are genetically engineered to be the ultimate survivalists - they're enhanced physical powers honed to cope with any form of external stress. With powers bordering on (and some far surpassing) the supernatural, the Apoc are truly the next stage in human evolution.
With the world hurtled backwards into a pre-industrial state, the armies did what they knew best and relied on their training - those soldiers stationed abroad relying on their field survival skills, and those at home "on base" reverting back to attempting to reestablish posts of command and centralized society to the best of their abilities. 
After centuries of forced separation, a gradual rift opened between these two groups and a natural animosity along with it - growing steadily as one side either sought what the other had or blamed them for their current condition. These two groups, known as High-bred (for the "on base" members) and the Churl (for the "in the field" soldiers) also began to evolve into two strikingly different groups.
While all Apoc are human at their core, they do possess genetic manipulations which make them decidedly more than merely human - while some of these manipulations were intended by the Apocs' "Makers", others have emerged at their own pace over the many years which have passed since the apocalyptic event. These differences manifest in widely different ways:
High-bred
Only via observation of their feats can anyone discern that the High-bred are anything other than run-of-the-mill members of the military. Much like their ancestors, High-bred prize themselves on their cleanliness: usually keeping their hair short, staying physically clean and clean-shaven, and they bear their uniforms and insignia with pride. In fact, while it might seem incongruous with their shattered world, the Apoc High-bred seem to take a measure of pride in keeping these uniforms clean and in good working order - many see it, after all, as the only thing that separates them from the "unwashed and naked savages" known as Churls. While the flags of the nations that destroyed the world are now all but gone, High-bred proudly bear the insignias of rank, unit and base - seeing these tightly knit groups as the only family that they've ever - or will ever - have. 
In addition to their enhanced physical capabilities (which are nothing, if not impressive), Apoc High-bred usually wield a wide array of weaponry ranging from ancient nano-forged melee weapons (swords, axes, and maces) to firearms: anything from propellant-fired weapons to ion weaponry and railguns.
Churl
Unlike their divergent cousins, the Churl are the result of the savage side of mankind, scratching and scavenging for survival - and succeeding far beyond anyone's expectation. Churl are basically human in appearance, but generally their increased size or unusual proportions mark them as something more than human. Usually Churl tend to be far larger and more muscular than normal humans and often display elements of their unusual "mystical" nature through alterations in their physical appearance. Unusually, these mystical elements almost always center on a given Churl's ancestral homeland and those totemic or elemental ties found there. For instance, Churl that hail from a remote, volcanic island chain could display physical aspects that range from fish-like, scaled skin, to smoldering eyes of pure lava. Other than these mystical qualities, Churl wear or carry little that is non-functional: generally the bare minimum in the way of clothing and the maximum effect in the vein of weapons are chosen. In terms of specific weapons, Churl nearly always default to savage melee weapons - however, these weapons, as well, seem to possess a unique and mystical quality all of their own. Oddly, these weapons are often elements of ancient technology (such as hammers made from drive trains of old automobiles, shields built on the framework from wrecked truck bodies, or swords crafted from scavenged turbine blades) that have "transcended" in unusual ways (strange growth of crystals, transformation into obsidian or other materials, or the infusion of mystical powers).
Apoc Artwork by John Gonzalez