Mr Slater travelled to Sulawesi, Indonesia, and spent a week taking pictures of macaques in 2011.
It was meant to be a harmless selfie, designed to highlight the plight of the endangered crested black macaque.
But British photographer David Slater, who is at the centre of a bizarre court battle of the now infamous "monkey selfie", has revealed that being sued by a monkey has ruined his life and left him completely broke, The Daily Telegraph reports.
The 52-year-old from south Wales, who specialises in wildlife and conservation photography, said he has been left penniless after years of legal wrangling over whether he or the macaque owns the copyright of the picture.
Mr Slater, who couldn't even afford a flight to America to be at the court hearing on Thursday, said that he is considering giving up his career as a photographer, and becoming a tennis coach or a dog-walker instead.
"This would be a new venture for me. It would pay peanuts, but at least it would be more than photography," Mr Slater told The Telegraph.
"I am just not motivated to go out and take photos any more. I've had outlays of several thousand pounds for lawyers, it is losing me income and getting me so depressed. When I think about the whole situation I really don't think it's worth it."
Although his photograph of a grinning monkey is famous across the globe, Mr Slater says his income is around £100 every few months from image sales.
"Everything I did to try and highlight the plight of the monkeys has backfired on my private life," Mr Slater said. "I've had my life ruined".
Mr Slater travelled to Sulawesi, Indonesia, and spent a week taking pictures of macaques in 2011. He said he mounted the camera on his tripod, and then gradually persuaded the monkeys to press the shutter while looking into the lens.
In 2014 he asked Wikipedia to take down his picture after they published it without his permission, but the web giant refused and said that the copyright belonged to the monkey.
The US Copyright Office ruled that animals cannot own copyright but People for the Ethical Treatment of Animals (PETA) sued Mr Slater in 2015.
At a court hearing on Thursday in front of a federal appeal judge at the 9th Circuit in San Francisco, lawyers for Mr Slater said it was "absurd" for Peta to claim that the monkey was entitled to copyright on behalf of a monkey.
Angela Dunning, representing Mr Slater, told the court that PETA was "not even sure they have the right monkey", referring to Naruto. "It is absurd to say a monkey can sue for copyright infringement. Naruto can't benefit financially from his work. He is a monkey."
Andrew Dhuey, also representing Mr Slater, said PETA should pay all of his legal fees because "monkey see, monkey sue will not do in federal court".
Judge Carlos Bea asked why the case should not be dismissed and asked if anyone could point to the law which said "man and monkey are the same".
Judge N. Randy Smith said: "There's no loss as to reputation. There's no even allegation that the copyright could have benefited somehow Naruto. What financial benefits apply to him? There's nothing".
In spite of everything, Mr Slater said he does not regret taking the picture of the monkey. On the contrary, he said he is "absolutely delighted".
"It has taken six years for my original intention to come true which was to highlight the plight of the monkeys and bring it to the world," he said.
"No one had heard of these monkeys six years ago, they were down to the last thousands."
He said that thanks to the publicity that his "monkey selfie" attracted, impoverished locals no longer shoot or eat macaques because "The locals used to roast them, but now they love them, they call it the 'selfie monkey'," he said.
"Tourists are now visiting and people see there is a longer-term benefit to the community than just shooting a monkey."