Andrew Oberle, a 26-year-old Texas graduate student, went to South Africa hoping to find ways to help chimpanzees, but now he is fighting for his life after the animals he was trying to protect turned on him in a violent attack.
Oberle, who is studying anthropology at the University of Texas at San Antonio, was leading a tour at the Jane Goodall Institute Chimpanzee Eden near Johannesburg Thursday when reports say he left the group and crossed one of two fences separating him from the animals.
When he neared the second fence, which was electrified, two chimpanzees reached underneath and pulled him by his feet into their enclosure.
Oberle was attacked by the animals and dragged half a mile before armed guards and staff members were able to enter the enclosure and rescue him.
"The chimps were still out there. ... He was curled up in a little ball," Lloyd Krause, an ambulance service manager who entered the enclosure to remove Oberle, told ABC News Friday.
Krausse said Oberle was mauled from head to toe before rescuers could reach him and the chimps.
"Those that were still in the enclosure had charged the fence a number of times on our arrival, so we did realize they were quite hostile at that point," he said.
Oberle, who suffered from severe bite wounds, underwent surgery at the Mediclinic hospital in Nelspruit, 180 miles from Johannesburg.
He is still in critical condition, but doctors say his vital signs have stabilized.
"The doctors are satisfied at the moment ... with the patient's condition," said Carmen Savva, the hospital manager overseeing Oberle's recovery in Nelspruit.
"He's responding better than expected," she said.
The attack is yet another reminder of how dangerous chimpanzees can be, despite their Hollywood image as fun-loving mischievous pranksters.
Stephen Ross, a chimp expert at Chicago's Lincoln Park Zoo, said the primates go through changes on their way to becoming adults.
"As they move through adolescence they become very, very interested in things like power and hierarchy," he said. "It's at this point that they become especially dangerous. They're no longer these small little furry creatures that you can carry around."
He said these particular primates may have had a bad behavioral background, because most had been abused by humans in one way or another.
"These are guys that have been taken from their mother as a result of the bush meat trade, perhaps raised as pets, and not housed very well," he said.
In a statement, the Goodall Institute said, "This is a terrible tragedy that should never have happened. ... All our thoughts and prayers are with this young man and his family."
The university said in a statement Friday that "our hearts go out to Andrew and his family."
David Oosthuizen, the institute's executive director, said the sanctuary had been closed temporarily after the attack.
Edwin Jay, the institute's chairman, said the two chimpanzees involved in the mauling would be returned to the enclosure after an investigation into the incident.
ABC News visited the sanctuary in 2009, where the director, Eugene Cusson said the animals are not only dangerous, but can be unpredictable after a life of abuse.
"If you were to go over into this enclosure right now through this hatch, I guarantee you 100 percent chance of fatality ... that you would be killed," Cusson said at the time.
As Oberle fights for his life in the hospital, his facebook page reveals he was aware of how aggressive and unpredictable the chimps could be. One photo in particular comes with the caption: "....He is a handful… luckily no one has bit me."
Oberle's mother, Mary Flint of St. Louis, told the AP Friday that he'd been in South Africa since May and that he'd passionate about chimpanzees since the seventh grade when he'd seen a film on Goodall.
Andrew Oberle Sr. also spoke of his son's dedication to the study of primates.
"He's put a lot of work into it and I just don't think he wants that to go to waste, because that is what he wants to be doing," Andrew Oberle Sr. told ABC News Radio.
ABC's John Muller, ABC News Radio and The Associated Press contributed to this story.