Boston ? Eunice Kennedy Shriver, the presidential sister who founded the Special Olympics and helped demonstrate that the mentally disabled can triumph on the field of competition and lead rich and productive lives outside the walls of institutions, died Tuesday at age 88.

Shriver had suffered a series of strokes in recent years and died at a hospital on Cape Cod in the company of her husband, her five children and her 19 grandchildren, her family said.

“She understood deeply the lesson our mother and father taught us: Much is expected of those to whom much has been given,” said her sole surviving brother, Sen. Edward Kennedy, who is battling a brain tumor.

She was also the sister of President John F. Kennedy and Sen. Robert F. Kennedy; the wife of 1972 vice presidential candidate R. Sargent Shriver; the mother of former NBC newswoman Maria Shriver; and the mother-in-law of California Gov. Arnold Schwarzenegger.

Shriver was credited with helping to bring the mentally disabled into the mainstream and transforming America’s view of them from institutionalized patients to friends, neighbors and athletes.

Her efforts were inspired in part by the struggles of her mentally disabled sister, Rosemary, who was given a lobotomy at age 23 and spent the rest of her life in an institution.

At the time, those with mental retardation were often a secret source of shame to their families and were quietly put away in institutions, out of sight and out of mind.

Shriver revealed her sister’s condition to the nation during her brother’s presidency in a 1962 article for the Saturday Evening Post.

“The truth is that 75 to 85 percent of the retarded are capable of becoming useful citizens with the help of special education and rehabilitation,” Shriver wrote. “Another 10 percent can learn to make small contributions, not involving book learning, such as mowing a lawn or washing dishes.”

Realizing they were far more capable of playing sports than the experts said, Shriver in 1968 started what would become the world’s largest athletic competition for the mentally disabled. The first Special Olympics — a two-day event in Chicago — drew more than 1,000 participants from 26 states and Canada.

Now more than 3 million athletes in more than 160 countries participate in Special Olympics. The games have given rise to countless uplifting stories of success against great odds.