Librarian

Librarians are huge, ape-like mutants in the novel and game Metro 2033. The librarians gained their name because they, unlike most mutants in the series, can only be found in the Moscow State Library. They are believed to be intelligent, as they can mimic human speech patterns almost perfectly, work in packs of two to four to when hunting and at least one used ammunition as bait to lure Artyom, the protagonist of the series, towards a hole in a wall where it attempted to smash him through from the other side. They are also territorial and will defend the library with their lives.

Appearance
Librarians look similar to ordinary gorillas in both posture and overall appearance. Their arms are longer and skinnier, however and they are slightly taller. The hands have two long fingers and a thumb while their feet have two equally long normal toes and a much shorter back toe, or dewclaw and they have pointed ears. The upper lip of a librarian hangs low enough to cover the creature's shark-like teeth. The most common kind of librarians are covered in grey-blue skin and are found all over the library, preferring the top floor. They are curious and will agressively charge a supposed threat, though they will back down if the target doesn't run, turn their back on the librarian or shoots anywhere near it. They can be stared down but a shot will send them into an aggressive state that won't end until the trespasser or the librarian in question are killed. In the archives underneath  the library are a breed of librarians known as Black Librarians. These creature have thick, black fur covering all their body and a missing upper lip, revealing rows of sharp teeth. The head of this breed is also deformed and covered in tumorous bulges.

Powers

 * Superhuman strength - A common librarian has strength on par with the creatures referred to by the people of the Moscow Metro as Demons. A black librarian is even more powerful than a common librarian, able to crush a human skull with ease.
 * Quasi-Intelligent - As stated before, Librarians are smart enough to percieve threats, lay basic traps and mimic human speech patterns. Whilst it is unknown if they can understand the words they speak, the original novel suggests that they do, with a librarian telling Artyom to go away, after mortally wounding one of his companions, Daniel, using the dying Daniel to shield itself.
 * Superhuman Endurance - It is advised by members of the Stalker and Ranger factions to stare these creatures down because they are able to shrug off most attacks without a problem. Headshots from an automatic shotgun or the Hellsing pneumatic crossbow can kill it in roughly 6-8 shots but otherwise, they are best avoided.