Richard Thornton, a US Olympian and Bay Area swim coach, died Thursday at the age of 65. 

Thornton died after collapsing on a beach in Santa Cruz County as he prepared to go surfing, his brother told ABC 7. 

A surfer rides a wave in Half Moon Bay

A surfer rides a wave at Mavericks on December 17, 2018, in Half Moon Bay, California. A giant swell brought waves of up to 50 feet high to Northern California.   (Ezra Shaw/Getty Images)

"He was following his buddy down the steps," said Marc Thornton, Richard's brother. "His buddy jumped in the water, looked up for Richard, and Richard was just standing there at peace not clutching his heart or anything and he just kind of collapsed into the water."

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His family said he had been receiving treatment for multiple myeloma, but the exact cause of death is not known. 

Thornton qualified in the 200 freestyle for the 1980 Summer Olympics in Moscow but did not attend, as the United States led a boycott of the games, according to Cal men’s swimming and diving.  

US Olympian swimmer and coach Richard Thornton pictured shirtless, smiling, at the beach in the summer of 1980 in black and white

Richard Thornton pictured in summer 1980  (Kenneth Grimes/Thornton Family/Facebook)

From 1977-1980, he attended the University of California at Berkeley, where he was a two-time All-American and a national champion. 

"We are heartbroken to learn of the passing of Cal Swimming great Richard Thornton," Cal athletics posted to X. "Our thoughts are with Richard’s family, friends, and all of those he impacted in the Cal community."

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Thornton became the head coach of the San Ramon Valley Aquatics in 1984, and he coached several future Olympians. 

Marc Thornton told KTVU Fox 2 that his brother had been a mentor to many young swimmers. 

Kate Douglass competes for the U.S.

Kate Douglass of the United States competes in the Women's Medley 200m Semifinal during the 20th World Aquatics Championships at the Marine Messe Hall A in Fukuoka (Japan), July 23, 2023  (DBM/Insidefoto/Mondadori Portfolio via Getty Images)

"He would sit down with them personally and actually understand them individually and help them achieve what they could achieve," his brother said. 

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"He was very open and earnest. He just cared about people on an individualized basis, and that's why people I think looked up to him as a mentor."

Thornton was the head coach of the 1995 U.S. World Championship and is survived by his wife and daughter.