Gorillas would spawn in jungle biomes in packs of 3-7, with one silverback who is the leader. The silverback is the largest and most hostile.
If you win the silverback’s trust by bringing the pack bananas or meat, helping to protect the young, etc, eventually you can befriend the pack. They will protect you when you are near by, and will occasionally bring you things like bananas. To maintain this friendship you have to give the silverback something once every 2-3 days.
If you hit a gorilla, the whole pack becomes hostile. Some packs protect temples, and they are spawned hostile.
A hostile gorilla does 3 hearts of damage, a hostile silverback does 5. A gorilla protecting you does 2 hearts of damage, a silverback protecting you does 4.
When you kill a gorilla you get black wool and leather, if you kill a silverback you also can get grey wool. A gorilla has 10 hearts and a silverback has 15.
To breed them, the pack has to be friendly towards you and you have to feed them a banana. There is a 1% chance that they will have twins, in which case the pack would be even kinder towards you for the next 3 days and you wouldn’t have to give something to the silverback during that period.
There is a 5% chance when you breed gorillas that it will favor you, leaving the pack to follow you instead. Once that gorilla has grown, there is a 50% chance you can ride it and a 50% chance you can put a chest on it. This gorilla will not protect you and you can only have one at a time.