The gorillas are a pet project by Clayton Holdren in an attempt to recreate pre-War gorillas and hopefully other species. There are two specimens, and both are actually synths designed in the form of the Silverback gorilla. This is revealed upon talking to Clayton, who brings up the gorillas while introducing the Sole Survivor to Bioscience during Institutionalized.
The ghoulrilla is a ghoulified gorilla living in Nuka-World. They are most likely offspring of the original gorillas kept in the Safari Adventure zone of the park. Years of radiation and inbreeding have turned them into ghoulish creatures.
They are synthetic gorillas, natural in appearance and realistic in behavior, but robotic at base level.
Ghoulrilla is very similar in appearance to the gorilla in the Institute. However, these have scabs and scratches located around the body, with scraps of fur torn out as well. The face is very rough and worn, with many skinless patches. The eyes are very dark, with no pupil or completely pupil, and it is very peculiar. They range in size from smaller to very large.
The gorillas are largely passive to the player character and wander around their terrarium. However, during A House Divided, their enclosure can be opened, where they will be hostile to everything, including the player character. This same occurrence can happen if the The Nuclear Option quests are carried out against the Institute. Also, placing an Institute beacon during Airship Down may spawn a couple of them to the player character's side. Upon breaking into the Bioscience division, the cage will then be opened and the gorillas will attempt to assist the synths in combating the Sole Survivor and whatever faction they chose to side with.
All ghoulrillas are passive by default, however attacking them will incite them to attack. Attacking Cito will also cause any ghoulrillas in Safari Adventure to attack the player. Similarly, attacking The Pack will cause their ghoulrilla pets to attack.
In Nuka-World, the player can find that the pre-War gorillas in the Safari Adventure attraction have undergone ghoulification. The ones remaining there are trapped in a small shelter with Cito due to the gatorclaw population in the area. Some are located in The Pack headquarters, and are used as combatants in the arena, fighting against mole rat and other ghoulrillas.
With Wasteland Workshop installed, gorillas can be caught in a cage and then released to serve and protect the settlement. They are docile by default, add 20 bonus happiness points to the settlement (as much as a tier 2 bar or clinic) and 10 points to the defense value (as much as a deathclaw). However, the player character must have completed The Nuclear Option (with any faction) and given the evacuation order to be able to build the cage.
The captured gorilla will level together with the Survivor, just like Dogmeat. Therefore they are enormously helpful in defending settlements.
It is also possible to obtain a docile gorilla in the base game. There is a 10% chance that the refugees in the quest Resettle Refugees will have a pet gorilla.
↑Scripts/Base/Fragments/Quests/QF_MinRecruit09_00164167.psc line 31: ; chance for pet gorilla :) if Utility.RandomInt(1, 100) > 90 Alias_Refugees.AddRef(Alias_SettlementSpokesman.GetActorRef().PlaceAtMe(WorkshopGorilla)) endif