Wights are a subset of Humanity caused by mutation.
In a handful of places, people did not have adequate shielding from Gamma Radiation, which permanently affected their bodies. The neurons and DNA of these individuals were damaged, and their neurotransmitters are produced at a less efficient rate. While they can still move and absorb oxygen efficiently, these transmitters are not plentiful enough to maintain dermal elasticity, and thus their skin often falls victim to necrosis, and is dry, giving them an almost mummy-like appearance. In addition their cartilage repair is stunted, causing joint problems, disc issues, and also causing their noses to rot away. This traits are permanent, as a result of damaged DNA (Gamma Rays caused these changes quickly, but just as quickly dissipated), and also inheritable.
In addition their subcutaneous flesh builds up a carbon compound with high density (theorized to be a iron, and which produces a bile-like scent. This compound serves a function similar to melanin, however instead of UV radiation, this compund blocks Alpha and Beta particles, allowing them to shoulder radiation levels that would kill normal humans. It is important to note that Gamma Radiation is still immensely lethal to them.
Most Wights appear as leathery zombies, with dry flaky skin, rotted away in some patches, and rougher and calloused in others. In addition, first generation Wights all lack hair (though second generations have normal hair), and many Wights have greyed irises, the result of acute glaucoma. Another notable feature is the gravelly voices of Wights.
Since the Great Nuclear War, more people have had run-ins with Wights. Wights are often second-class citizens, being viewed as Bewitched or Cursed by superstitious folk. In the Deep South, as well as the Insular States, Wights are not allowed to own land, nor live among pure humans, with the Exception of the Iron Hills and Kentuck Empire, where they are not numerous enough to warrant laws being passed about them.
It is notable that alongside Blacks, Hispanics, and Native Americans, Wights are kept as Slaves by the Klu Klux Klan.