Radstags descended from the common deer in the Wasteland after their ancestors were exposed to great quantities of radiation in the fallout of the Great War. Due to this longstanding exposure to radiation, radstags, like brahmin, have two heads.

They are usually brown-furred and patchy in places, with small pus-filled cysts from radiation, which most often cover the flanks, feet, heads, and snouts. The cysts more frequently appear on the rabid and glowing varieties and can cover most of the body. Radstag yearling coats are more colorful than those of adult radstag and feature white spotting, similar to the fawns of their deer ancestors.

Radstags can be found across the Wasteland but are common in regions like the hub or the irradiated forest. They generally pose little to no threat but will attack if they feel trapped or threatened.