Feral ghoul

Feral ghouls (also known as "mindless zombies," "ghoul crazies," "feral necrotic post-humans" or "zombies") are ghouls (necrotic post-humans mutated by radiation) that have lost their ability to reason and have become aggressive. This has caused much discrimination toward other ghouls that have retained their mental faculties by human Wastelanders. Feral ghouls are a great source of bobby pins and caps. So if you're running low on either item, make sure you search some dead ghouls.

Biology
The brain structure of a feral ghoul indicates that the regenerative ability of the neurological system that affords "normal" necrotic post-humans their longevity does not extend into the higher reasoning functions of the brain itself. This condition is referred to as "ferocious post-necrotic dystrophy", according to the ghoul physician Doctor Barrows. M.A.R.Go.T. also states that feral ghouls have no internal body heat.

As the reasoning and critical thinking portions of a ghouls cerebrum deteriorate, the ghoul subject becomes increasingly hostile, giving in to a carnal need to feed as opposed to the capacity for thinking and reasoning that a non-feral ghoul retains. It remains unclear exactly what precipitates this change in neurobiology and psychology, but anecdotal evidence seems to indicate that non-social ghouls, or those in isolation, are more prone to the condition.

It is also quite possible that this is a gradual process, meaning that eventually all ghouls would succumb to this condition. However, considering the existence of ghouls that have been born prior to the Great War two centuries ago, it is quite possible that this theory is bunk, or that the rate of degeneration is dependent on the individual affected and surrounding environmental factors.

They give a high-pitched screech when attacking 'prey' (AKA You and NPCs). This can be useful for dark areas or areas with lots of items blocking your view.

Behavior
Feral ghouls often cluster together in dark, cool environments, like sub-basement-levels or totally underground areas, only occasionally leaving their normal hunting grounds for time in the open air. However, the myth that ferals fear light is false. Occasionally, the player may encounter one or two ferals out in the open. Isabella Proud's research seems to confirm that feral ghouls do not fear or avoid light.

Frequently, ferals will wander from place to place, stopping at fallen prey to feed, but will immediately attack any and all non-ghoul creatures they come across. Upon detecting a non-ghoul, most ferals will make a high-pitched gurgle or screech, and set out to search the area. Upon sighting prey, they will often scream once more, alerting any nearby ghouls, and attack.

Ghoul Mask
One interesting note with ferals is that they seem to be fooled by very rudimentary means. The Ghoul Mask, seemingly nothing more than the hollowed-out head of a ghoul or several pieces of a human head stitched together, still seems to deter ferals from attacking.

When wearing the ghoul mask (or using a Stealth Boy) the player can observe relaxed feral ghouls' actions, including twitching, bending down, having fits or sniffing the air. If you are wearing the ghoul mask, ferals will often turn their head to the side and stretch their necks when you come near them, as if they are confused.

Note that Roy Phillips (Quest: Tenpenny Tower) tells you that if you get close to the ghouls they will "sniff" you out and attack you, even if you have the mask on. However, the ghouls will not attack you unless you remove the mask or provoke them.

Feral Ghoul
Feral Ghouls are the basic feral ghoul variant in Fallout 3; naked and noticeably weaker than standard human opponents, they are easily dispatched with one or two headshots from any decent weapon or a solid hit from a decent melee or unarmed weapon. Despite their shrill noise and remarkable speed, they are only truly a threat when they have the advantage of numbers, or when the player is at low level.

Feral Ghoul Roamer
Feral Ghoul Roamers wear what appears to be the remains of combat armor, and are somewhat tougher than standard Feral Ghouls, requiring more damage to be dealt to put them down. It is possible that Roamers are ghoulified U.S. soldiers as they wear tattered remains of Combat Armor.

Glowing One
Glowing Ones are the rarest of the Feral Ghouls. They have even higher durability than Feral Ghoul Roamers, and can take several hunting rifle headshots before expiring. Additionally, they periodically emit a 360 degree pulse of potent radiation (Around 25 rads per second) that damages human enemies and heals any nearby Ghouls.

Feral Ghoul Reaver
Feral Ghoul Reavers appear in the Fallout 3 add-ons Broken Steel and Point Lookout. They are much more combat-worthy than other ghouls, and have the ability to throw radioactive gore. Aside from the damage they can inflict, Reavers also have great endurance and boast one of the highest HPs in the game, being able to survive even attacks from the Fatman.

Swamp Ghoul
Swamp Ghouls inhabit the swamps of Point Lookout. Aside from their paler coloration, they are very similar to standard feral ghouls in both general appearance and combat abilities.

Endless Walkers
Endless Walk is the punishment in which a ghoul from the Reservation is stripped of every worldly possession, including clothing, and sent marching into the wasteland. No ghoul has ever come back from the Endless Walk (exiled from the Reservation Otto Stead was saved by governor Dodge at Hoover Dam). Another source of Endless Walkers in the Boulder area is the Crater, the remains of what was once NORAD.

Not all Endless Walkers end up scorpion food, at least not at first. On those rare occasions when one survives more than one year in the wasteland, they turn into wandering, voracious creatures on an endless quest for flesh. Due to their prolonged, open exposure to the desert sun, high radiation, and other hardships of the wasteland, these unfortunate ghouls, who were banished naked from the Reservation, look like walking, sun bleached chunks of beef jerky. Their constant exposure to the hot sun and high levels of radiation has caused their skin to toughen into natural, hardened leather, but at the same time, their ability to reason has been completely lost.

Appearances
Feral ghouls appear in Fallout (in random encounters, as "mindless ghouls"), Fallout 2 (as "ghoul crazies") and Fallout 3 (where they are actually named "feral ghouls" for the first time).