A tiny population of goats were introduced to the Capital Wasteland shortly after the Great War, after living underground with a small band of survivors, who set up a commune at the Hilltop Farm ruins. These goats had lead short lives on the surface, protected by the also short-lived residents of the Hilltop Farm ruins, with the residual radiation too intense for the goats, they died alongside chickens that had also been overwhelmed. The primary caretaker of the goats was most likely Miles, as he was the only one with farm experience.
Goats are long domesticated farm animals with many uses, they are bred for hide, milk, meat, fiber and even manure. They are hardy creatures, curious and intelligent, and are notorious for their unfussy diets. They are herbivorous but are all too willing to have a taste of that which is not typically in their diet, which could prove a useful asset in the grand scheme of survival.
Goats are mentioned only in Fallout 3 and are represented as tribal markings, classed as graffiti, in Fallout: New Vegas add-on Honest Hearts. Other mentions may be found in the Fallout series but only as insignificant dialogue references.
The well known 'goatee' beard, is a real life facial hair style, also offered in-game wherever the player character can set or alter their appearance, such as the gene projector in Fallout 3. It is based on the traditional Billy goat tufted chin.