Timothy Shriver's uncles included President John F. Kennedy, Senator Robert F. Kennedy and Senator Ted Kennedy, but he says it's his aunt Rosemary who wielded the most influence. Born in 1918, Rosemary had intellectual disabilities, a stigma back then.

"Her influence wasn't noticed by me or anybody else at the time," Shriver said, "but I came to realise the person most responsible for our family putting our hearts, our passion, our convictions into service, was Rosemary. The more I reflected on it, the more it struck me: She was the one who had the most power, the whole idea of service being joyful and not a burden, the idea of equality worth fighting for, worth dying for."

Rosemary Kennedy's intellectual disabilities remained a family secret for decades due to stigma. Ending this stigma has been the mission of the Shriver family and Special Olympics for more than 50 years.

The joy of public service will be fully on display July 25-August 2 when the 2015 Special Olympics World Games take place in Los Angeles, the first time the event has been held in the U.S. in 16 years. More than 7,000 athletes will compete.

Setting the Stage for the World Games

Shriver, Chairman of Special Olympics and author of "Fully Alive: Discovering What Matters Most" (Sarah Crichton Books, 2014), is thrilled by the locale. "Los Angeles is the center of great storytelling, of great drama, of creating cultural icons and cultural movements," he said. "Having the World Games in the U.S. at this moment is critical since we're trying to tell a new story to the world of inclusion, not exclusion."

He noted that there will be many entertainment heavyweights, from Hollywood luminaries to musical superstars, in attendance. A wide number of shows, such as "Entertainment Tonight" and "Good Morning America," are on board to bring athletes' stories to life. ESPN was named the event's official broadcaster and will show the opening ceremony as well as a nightly highlights program.

Eunice Kennedy Shriver, Rosemary's younger sister, actively began advocating for people with intellectual disabilities in the 1950s. In 1962, she and her husband, Sargent Shriver, who founded the Peace Corps, welcomed dozens of institutionalised children to a summer day camp in their suburban Washington D.C. backyard. Mrs. Shriver wanted to give the children a place to play together. Year after year, the Shrivers continued the tradition, their five children (Bobby, Maria, Tim, Mark and Anthony) pitching in to help.

The first official Special Olympics were held at Chicago's Soldier Field on July 20, 1968. Roughly 1,000 athletes were cheered on but there was little media attention.

"People with intellectual disabilities were invisible. It was more about opening people's eyes," Shriver said.

A Partnership That Makes a Difference

Mrs. Shriver approached Don Keough, Coca-Cola's president at the time, and he immediately put people to work on the project. "Coke has been a partner since the very beginning," Shriver said, "when it seemed unusual or even crazy for such a huge brand to get involved with a forgotten population. They understood the positivity of the movement. Don Keough and my mother created the first corporation-cause relationship and it became one of the most powerful in the course of the last 50 years."

Eunice Kennedy Shriver speaks at a 1978 Special Olympics press conference. Coca-Cola was the founding sponsor of the organisation.

From 1968 to 2015, the biggest change Shriver has observed is how Special Olympics has become a movement for everyone, not just for people with intellectual disabilities.

"Learning about the power of difference is unifying," he said, adding that today's millennials understand that message and embrace it with enormous energy. "Their cause is nondiscrimination, overcoming age-old evils of racism and sexism, clearing the blinders people have about sexual orientation. They care about the earth and the environment and justice and see it as a relationship-building idea, not necessarily a political idea, the way my generation saw it."

Big Lessons to Learn

Shriver, 55, grew up volunteering for Special Olympics, continuing through high school, college, graduate school, his years working in public and special education and later as a film and television producer. His wife and five children are also involved.

One of Shriver's TV projects, "The Loretta Claiborne Story," documents the inspiring saga of an athlete who was born poor, with visual impairments and intellectual disabilities. Yet she went on to win multiple Special Olympics medals, run 26 marathons and travel the world as a motivational speaker.

Loretta Claiborne is a celebrated athlete who was honored in 1996 with ESPN's ESPY Arthur Ashe Award for Courage.

Several years ago, Shriver accompanied Loretta Claiborne on a talk she was giving to scholars. "I was operating under the old paradigm that she was going to tell them she belonged, that she was smart and gifted enough to make it in the real world," he recalled. "She got up and spoke about her life and at the end of her remarks she caught me totally off-guard. She said, 'Come into my world. I don't want to join yours. Mine has no war. Sports are played with the spirit of joy and exuberance and affirmation, not anger or cheating or aggression.'"