The event was publicly spearheaded by Eunice Kennedy Shriver, whose brother Robert F. Kennedy had been killed only six weeks earlier, and was mounted with help from a small group of physical education teachers, disabilities experts and physiologists, including a Canadian professor, Frank Hayden, whose research helped convince Shriver that such an event was possible.

For years, parents and educators had believed that young people with Down syndrome and other intellectual disabilities were incapable of playing sports or engaging in physical activities. Dr. Hayden helped dispel that myth, showing that kids with special needs were hindered mainly by lack of opportunity. With guidance and encouragement, he argued, they could see improvement in physical fitness while also gaining social skills and confidence.

“My idea wasn’t to find the fastest runner with an intellectual disability,” he said. “It was to make them fitter and healthier, so they have the opportunity to live their potential.”

Dr. Hayden, who spent years championing the Special Olympics and spreading the movement to countries around the world — a quest that led him to call himself “the Billy Graham of the Special Olympics” — died May 16 at 96.

His death, in Oakville, Ontario, was confirmed by Canada’s Special Olympics organization, which said his “research was the spark that ignited the Special Olympics movement.”

“At the time, the prevailing literature indicated that this was just the way it was going to be: There was no way that kids with intellectual impairments would become more physically active, which would lead to healthier lifestyles and healthier outcomes,” said sports researcher Laura Misener, who holds an endowed chair named in Dr. Hayden’s honor at Western University in Ontario.

“He pushed that narrative aside,” she said, “and demonstrated that kids with intellectual disabilities could be involved in sports and physically active.”

Dr. Hayden never set out to become an expert on disabilities. But while finishing his graduate studies in the early 1960s, preparing to start a job as a research associate at the University of Toronto, he got a call from his new boss, who told him about a Rotary Club grant for a fitness study on children with special needs.

The grant would cover half of Dr. Hayden’s salary.

Was he interested?

After spending two days in the library, where Dr. Hayden discovered that there was virtually no published research on fitness and intellectual disabilities, he decided the answer was yes. “I figured that I would become an instant expert,” he said, “and that I had a blank sheet.”

Over the next few years, he worked with disabled children at the Beverley School in Toronto, leading them in sit-ups, running and jumping activities. The students were about half as physically fit as children without cognitive disabilities, he found, but no wonder: “They didn’t ever run, skate, play ball, didn’t play kick the can.”

Through patient coaching and an exercise plan, he found that the students could grow strong and gain confidence that helped them widen their abilities in other areas. He cited the case of a Beverley student who “learned to read because he played floor hockey,” since he “wanted to know what was being written about him in the school paper.”

Dr. Hayden drew on his research to write a 1964 training manual for people with intellectual disabilities, aimed at educators and parents. He originally intended to distribute 1,000 copies, he said. But the book took off, selling more than 50,000 copies and reinforcing his belief that there was a hunger for new fitness programs, and potential for a large-scale sporting event for children with special needs.

His initial proposal, for a Canadian national games tied to the country’s 100th birthday, went nowhere. But his efforts attracted the attention of Shriver, whose advocacy efforts were informed by her bond with her sister Rosemary Kennedy, who was born with an apparent intellectual disability and institutionalized after a lobotomy. Shriver and her husband, Peace Corps director Sargent Shriver, invited Dr. Hayden to their home and asked if he could organize a national games for the United States.