Back in 1990, a 135-pound chimpanzee named Jo-Jo slipped into water at the Detroit Zoo after being chased by another chimp. Dozens of visitors and zoo workers watched as he thrashed around helplessly.

There was a cable in the enclosure, designed to keep chimps from falling into the water. But on this fateful day, the cable didn’t do its job.

Truck driver Rick Swope stood in horror alongside his wife and three children. He saw the look on the 18-year-old chimp’s face and knew he couldn’t just stand back and do nothing. It were as if Jo-Jo was begging for an onlooker to come and rescue him — and that’s exactly what Swope did.

Now, think about this: Chimps have up to five times the strength of humans, the zoo enclosure was forbidden territory for visitors, and the enclosure was full of other apes that could turn aggressive at any moment. But without any hesitation whatsoever, Swope left his family and jumped into the forbidden ape enclosure. He grabbed onto the drowning creature, but quickly lost his grip. Despite the fact the water was only five feet deep, it was so dirty, he couldn’t see through it.

Visitors cheered on Swope as he grabbed Jo-Jo once again and pulled him onto the slippery shore.

“He was pretty lifeless, but you could see he was still alive,” Swope told the Chicago Tribune. “He was looking at me. I think he knew what was going on.”

Thanks to the 33-year-old truck driver, Jo-Jo survived and recovered. “It was no big deal, you know,” he said. “It didn’t take an exceptional person to do it. If it did, I couldn’t have done it.”