Eunice Kennedy Shriver, a member of one of the most prominent families in American politics and a trailblazer in the effort to improve the lives of people with intellectual disabilities, died early Tuesday morning at Cape Cod Hospital in Hyannis, Mass. She was 88. Her death, at 2 a.m., was confirmed by her family in a statement. A family friend said that Mrs. Shriver had been in declining health for months, having suffered a series of strokes.

A sister of President John F. Kennedy and Senators Robert F. Kennedy and Edward M. Kennedy and the mother-in-law of Gov. Arnold Schwarzenegger of California, Mrs. Shriver never held elective office. Yet she was no stranger to Capitol Hill, and some view her work on behalf of the developmentally challenged, including the founding of the Special Olympics, as the most lasting of the Kennedy family’s contributions.

“When the full judgment of the Kennedy legacy is made — including J.F.K.’s Peace Corps and Alliance for Progress, Robert Kennedy’s passion for civil rights and Ted Kennedy’s efforts on health care, workplace reform and refugees — the changes wrought by Eunice Shriver may well be seen as the most consequential,” U.S. News and World Report said in its cover story of Nov. 15, 1993.