The gorillas are a pet project by Clayton Holdren, whose goal is 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 Sole Survivor can read in the division's terminals that the gorillas react aggressively to perceived conflict, which may be a fault in their behavioral model.
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 have turned them into ghoulish creatures.
Synth gorillas are natural in appearance and realistic in behavior, much like gen-3 synths.
Ghoulrillas are very similar in appearance to synth gorillas. However, these have scabs and scratches located around the body, with scraps of fur torn out as well. Their face is very rough and worn, with many skinless patches. The eyes are very dark or lacking pupils. Their size varies.
The gorillas largely ignore 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 can also 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 character. Similarly, attacking the Pack will cause their ghoulrilla pets to attack.
The basic variant of the gorilla are made by the Institute and are the weakest variant in the game. With the Wasteland Workshop add-on, gorillas can be captured with cages and used for settlement defense.
In Nuka-World, the player character can find that the pre-War gorillas in the Safari Adventure attraction have undergone minor ghoulification. The ones remaining there are trapped in a small shelter with Cito due to the gatorclaw population in the area.
The ghoulrilla king shares the same looks as the basic ghoulrilla but the king is more powerful and rare to spawn. It first spawns when the player character has reached beyond level 50 and hasn't yet completed the Safari Adventure quest. The ghoulrilla king's affiliation is to Cito and acts as the leader of the ghoulrilla group. Cito has named him "Chris."
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 Sole 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.
Gorillas in settlements do not heal after a battle, unlike settlers and dogs.
↑Cito: "Chris big and strong. Chris help new friend and Cito. Chris is your biggest strongest gorilla friend." (Cito's dialogue)
↑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