Oliver the 'humanzee' was once considered to be the 'missing link' in the evolutionary chain.
His human-like walking style and features meant he was strikingly similar to one of us.
And resurfaced footage of Oliver has left viewers truly terrified.
Watch below:
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Oliver was a chimpanzee who was caught in the Democratic Republic of Congo and acquired by trainers Frank and Janet Berger in 1970.
Due to some physical and behavioural features, many considered him to be a human-chimp hybrid - otherwise known as a ‘humanzee'.
Along with having a small head, his face appeared to be flatter than that of an average chimpanzee.
Oliver also had a pronounced nose and would walk upright on two legs, rather than on his knuckles like a chimp.
As well as him having a bald head, Oliver lacked the chimpanzee’s trademark short, white beard and pronounced forward jaw.
Instead, he had pointed ears, placed much higher than usual whilst even having freckles.
Some thought he was the missing link, which is not a term used by biologists.
That's because the term it implies the evolutionary process is a linear phenomenon and that forms originate consecutively in a chain.
Instead, the term 'last common ancestor' is preferred and scientists said that Oliver was not a human-chimpanzee hybrid.
Commenting on the resurfaced footage, one viewer said: "Woah I remember this really freaked me out."
"I'm not going to sleep after seeing that face. It's the scariest face. Ever."
In 1975 Frank and Janet sold Oliver to a Manhattan lawyer called Michael Miller, who gave Oliver to Ralph Helfer, a partner in a small theme park called Enchanted Village in Buena Park, California.
He was then purchased by Buckshire Corporation, a Pennsylvania laboratory leasing out animals for scientific and cosmetic testing, in 1989.
Now partially sighted and arthritic, Oliver was then moved to open air cage Primarily Primates in Texas.
According to Primarily Primates: "Oliver was a gentle soul who brought out the kindness in other chimpanzees."
He also became sexually attracted to his carer and preferred humans over chimps.
“He loved coconut sorbet — that got the biggest hoots and hollers,” one caregiver said in 2012.
“But if he didn't like something, he'd hand the bowl back to you — like the time he tried sugar-free pistachio pudding.”
Sadly, in June 2012, Oliver 'was found resting motionless' in filmmaker Andy Cockrum's hammock.
He passed at the age of 55.
"Although Oliver was gone, he was certainly not forgotten. Plans to create an enrichment habitat were in the works and it was decided that the new structure would be situated where Oliver lived during his time at Primarily Primates," they added.
"Two years after his passing, Primarily Primates and Friends of Animals were able to unveil the new habitat which was dubbed Oliver’s Playground."
Anish Vij