Trogs reside in The Pitt (formerly Pittsburgh, Pennsylvania). Due to the town's infection with the Troglodyte Degeneration Contagion, around 25% of the populace have transformed into these wild, chattering monstrosities, hiding in the darkness and attacking anything on sight. However, their idle chatter suggests that they still have some shred of intellect, such as murmuring thanks upon death, or random words such as 'kill'. Still, all evidence indicates their degeneration overpowers all their humanity, as they will kill even friends and loved ones with savage violence (such as the case between Billy and his brother, John-John.)
The following is based on Van Buren and has not been confirmed by canon sources.
The trogs of Van Buren differ greatly, especially in the sense that they retain a large portion of their intelligence. The trogs of Hoover Dam, while not pleasant to look at, look much more human than their Pitt counterparts. A trog's skin has a dull white color and their hair (when present) is a yellowish color due to a deficiency of melanin. The trade-off is that their skin became thicker, making them more resilient to their hazardous environment. They are, however, very sensitive to light, a trait they share with their more animalistic brethren from The Pitt.
The Hoover Dam trogs were nomadic at one time, thanks to a cave-in at their previous dwellings. Before Dodge and his troops came to Hoover, Billy-Bob and his trogs took up residence in Baseline, figuring it was pretty secure from caving in. No one argued with the trogs, and when Dodge came to Hoover, he asked if they would help out Otto with the maintenance in exchange for food, goods, and water. The trogs accepted, content to mosey around Baseline, making sure every light was flashing correctly, ever since.
As a direct result of their disease, trogs are hairless, naked, primate-like creatures with long, gangly arms and legs. Their skin appears raw and wrinkled, and their faces are scrunched into permanent scowls, with their teeth constantly bared. They have four fingers (including opposable thumb) and four toes, and their feet appear to be in the process of turning into "hands," adding to their primate-like appearance. They crawl on all fours (somewhat similar to frogs). They have no external genitalia or any other visual clues to their sex, making mammalian sexual reproduction unlikely; Wernher implies that they are capable of sexual activity, however, this may be deliberate as the showing of genitalia would result in a higher maturity rating for the game.
Despite their savage appearance, trogs are capable of hunting in packs like wolves. While some may simply charge at targets head-on, others will attempt to sneak up on the prey from behind or above. Their speed is almost on par with a yao guai, though they are able to leap even farther.
Trog packs usually circle their prey, slowly closing in, and the target can be quickly surrounded if they are unwary. Although trogs are known to be extremely photosensitive, in-game trogs will actively pursue their prey through light and dark alike. However, they will only spawn in darkened areas, such as the steelyard, power plant, and abandoned apartments; not in lit places such as Uptown, even though they are one door away from its streets.
Trogs are weaker than standard humans; a basic trog is on par with a basic feral ghoul, and even the powerful trog brutes and savages are still only on par with standard raiders in terms of health. However, they are much faster than normal humans, have fairly powerful melee attacks, and rarely hunt alone. Additionally, trogs are usually fought while the Lone Wanderer is poorly equipped, as their equipment is taken away upon entering The Pitt, and good weapons and armor can be hard to come by in The Pitt until the Lone Wanderer finishes The Arena and enters Uptown.
These trogs are the smallest and weakest of the trog family. However, they are still quite fast and may overwhelm anyone unaware of their presence. Headshots from decent weapons are usually fatal. They are one of the weakest creatures in the game (on par with bloatflies or radroaches in terms of health and attack damage). This type of trog will be encountered primarily at level 7 and below.
Trog brutes are the most commonly encountered trogs on very hard difficulty. They are only slightly larger than regular trogs but have almost double the health. Their attack is twice as powerful as their standard variants.
These trogs are the strongest and most powerful trogs in The Pitt. They are encountered rarely but are essentially trog brutes with slightly more health. Although only slightly tougher than trog brutes, trog savages have powerful melee attacks similar in damage potential to those of a giant radscorpion or mirelurk hunter.
It seems most trogs carry exactly one item. Bobby pins are very common, as well as single doses of chems and various miscellaneous items.
When talking to Midea in her house for the first time, the Lone Wanderer can ask either what a trog is or imply that it is a fish. They can also ask if they are like a super mutant, to which Midea will reply asking what a super mutant is.
When facing a trog, they will sometimes mutter words like "hate," "kill" and "food," suggesting that trogs have some semblance of their sanity or human capabilities left, but are unable to fight their animalistic hunger. Some can even be heard muttering "...peace" or "thank you" right before they die. This does not invoke any karmic changes for the player character, however.
In Latin, the word "troglodytae" means "cave dwelling people" and is now used to describe someone who is reclusive, uneducated, or that lives underground.
The concept of the trog is very different in The Pitt from the original concept in Van Buren. This can be attributed to being from different developers as well as there possibly being different forms of trogs. However, since trogs from The Pitt are the only ones to appear in a published game they are the only ones that are canon.