As The Gorilla Foundation becomes entangled in another legal dispute, the non-profit's complicated past has once again been re-thrust into the spotlight.

Namely, the strange behavioral habits of its most famous - an allegedly rather kinky - former resident, Koko the signing gorilla.

Trained by Francine 'Penny' Patterson, Koko began 'speaking' American Sign Language at aged 1.

And for the next 46 years, the incredible creature continuously stunned audiences and A-list celebrities alike, befriending stars such as Robin Williams and William Shatner.

Koko began learning sign language aged 1 under the care of Francine Patterson (right). Over the next 48 years she continued to stun audiences around the world

However, a sexual assault lawsuit filed by two former employees of The Gorilla Foundation in 2005 revealed an entirely different side to the prized ape.

For all her brilliance, over the years Koko quietly developed a series of alarming anti-social tendencies, including an obsession with female nipples.

Kendra Keller and Nancy Alperin claimed it became such an obsessive fetish that Fancine Patterson 'pressured' the pair to 'engage in the sexual act of removing their clothing to expose their breasts' to Koko.

The lawsuit claims the request came from Patterson after a brief signed conversation with Koko.

'Oh yes, Koko, Nancy has nipples. Nancy can show her nipples,' Patterson is alleged to have said on one occasion.

A lawsuit filed in 2005 by Kendra Keller and Nancy Alperin (pictured left to right in 2004) claimed that Patterson pressured them to show Koko their breasts to appease her nipple fetish

Patterson insisted Koko's pervasive interest in their nipples was strictly non-sexual, and said it was a natural way to bond with her

In another instance she reportedly said: 'Koko, you see my nipples all the time. You're probably bored with them. You need to see new nipples. I will turn my back so Kendra can show you hers.'

Patterson allegedly told the claimants that exposing their breast's to Koko was a 'normal component to developing a personal bond with the gorilla.'

The trainer insisted Koko's pervasive interest in their nipples was strictly non-sexual.

Regardless, Kendra and Alperin refused to go through with the act, but depositions filed in the case revealed other employees had acquiesced to the gorilla's repeated requests.

And an AOL interaction between Penny and Koko on March 14 1998 showed the extent of her obsession with nipples.

As Penny tries to communicate with Koko, the gorilla repeatedly replies 'Nipple' to each of her questions.

The case was settled out of court a number of months later.

Koko died on June 19, 2018 aged 46.

Papers from the lawsuit claim a number of other employees were said to have exposed themselves to Koko, under both the gorilla's requests and Patterson's instructions

Now though, The Gorilla Foundation is ensnared in another legal battle, this time with the Cincinnati Zoo.

The Zoo had loaned the foundation a silver-back, named Ndume, in 2000, under the hope he would be able to mate with Koko.

The foundation claimed Koko had selected him after watching several videos of other gorillas.

'Koko love - bring,' she allegedly signed.

However, Koko is said to have shunned Ndume shortly after his arrival - even tormenting him on occasion by urinating on him.

Cincinnati Zoo are now attempted to reclaim the last of the Gorilla Foundation's apes, having loaded Ndume to Patterson in 2000 in an attempt to mate with Koko. It failed and the pair had to be seperated

The animals were eventually separated and now the zoo wants him back.

Like Koko, he understands a lot of spoken English, but Ndume was never part of the foundation's plan to achieve inter-species communication.

Patterson argues that transferring Ndume - who is the last gorilla at her foundation - would be a risk to his health and could kill him.

'He is with a strong family support group of human great apes', she said in a 2018 letter to the zoo.