Many of Anthony Ervin‘s competitors were just learning to read and write the last time he won a gold medal, at the 2000 Olympics in Sydney, before he abruptly retired – but they know how to spell his name now.

On Sunday, Ervin anchored the qualifying leg that put the U.S. in position to win gold in the 4×100-meter freestyle relay, earning him his first medal since he was a teenager. This Thursday he will compete in the 50-meter freestyle – the shortest, fastest race in aquatics.

Get push notifications with news, features and more.

Few would have expected that Ervin – at 35, the oldest American man to swim an individual Olympics event since 1904 – could have made such a comeback.

“It’s fair to say nobody has been through what he has,” U.S. swimming coach David Marsh tells PEOPLE. “But Anthony’s got the most efficient freestyle I’ve ever seen. That’s been the case since he was young. He’s just a barracuda in the water.”

Early Dominance

Ervin was a standout swimmer growing up in Valencia, California, with a lean, uniquely American look – a genetic mix that includes Jewish, Native American and African-American roots. Ervin developed symptoms of Tourettes just before high school. The physical tics and disorientation made him feel like an outcast, he recounts in an inspiring, humorous and often profound biography, Chasing Water: Elegy of an Olympian published this summer and written with Ervin’s friend Constantine Markides.

He controlled the tics with medication and went to Cal Berkeley, where he excelled in the short races. Ervin was 19 when he became the fastest man in the water, setting a world record of 21.21 in the 50-meter at the NCAA Championships. That summer in Sydney, he won Olympic gold in the 50-meter, in a dead heat with fellow American Gary Hall Jr.

He shocked the swimming world when he retired two years later, at age 22. If his coaches expected a brief hiatus while Ervin dealt with the phenomenon known as “swimmer’s burnout,” they were mistaken. Ervin went off the deep end.

Losing His Swimmer Label

He had already tried to commit suicide by swallowing a handful of tranquilizers, and he nearly killed himself more than once riding a motorcycle while high on LSD and cocaine. After his retirement, he disappeared from the swimming community. In 2004, he got fired from a tattoo parlor in Berkeley. He played guitar in a band called Weapons of Mass Destruction and briefly sold equipment at a music shop. In 2005, he became so moved by the plight of tsunami victims that he sold his gold medal for $17,000 and donated the money to relief efforts. Maybe with an eye to a comeback, he inked his right arm with a Japanese-style phoenix, the mythical bird of destruction by fire and resurrection.

But instead of training for either the 2004 Olympics in Sydney or the 2008 Olympics in Beijing, Ervin went deeper into the rock-and-roll lifestyle of drugs and late-night music gigs. He dabbled in Buddhism and cross-dressing, he writes in his book. He stopped telling people he had ever been a swimmer, much less an Olympic champion.

Road to Rio: How Did Team USA Train for the Olympics?

“The oppression of my former swimming identity loses its hold on me,” Ervin writes. “I am no longer Anthony Ervin the Swimmer, but Tony, just another guy in a band.”

His mother, Sherry Ervin, was devastated. “I don’t think Anthony realized just what he sacrificed,” she says. “I don’t think he understands it even now.”

A former Cal teammate got Ervin a job giving swimming lessons to children in New York City, and Ervin briefly entertained the idea of returning to competitive swimming. But more years passed, as Ervin, often homeless, lived on friends’ couches and neared age 30. Ervin hit an “absolute low,” according to a friend, when after years of abusing himself on painkillers and other drugs, he was hardly able to rise from a sofa for days on end.

“I didn’t think he’d come back,” Marsh tells PEOPLE. “He’d lost all his muscle. He was a shell of himself as an Olympic champion.”

Recovery and Comeback

Ervin’s slow turnaround began in 2008, when he re-enrolled as an undergraduate at Cal Berkeley. He studied literature and discovered a passion for medieval texts. And finally, in 2011, he wanted to swim again.

When he announced his intention to train for the 2012 Olympics, though, coaches were skeptical. “I thought it might be more of a lovely gesture,” Marsh says. “I didn’t expect him to actually make it back to the Olympics.”

But Ervin did it, and placed an impressive fifth in the finals of the 50-meter freestyle in London with a personal-best time, leaving his coaches shaking their heads.

“It’s his ability to make changes, both in his life and in the water, that makes him special,” longtime coach Mike Bottom tells PEOPLE.