Sargent Shriver, the first United States Peace Corps director and brother-in-law to President John F Kennedy, has died aged 95.
His son, Anthony Kennedy Shriver, said he died on Tuesday after two days in hospital.
A statement said Mr Shriver, who had Alzheimer's disease in his final years, was surrounded by his five children and 19 grandchildren when he died.
Mr Shriver, who was George McGovern's vice-presidential running mate in 1972, married Eunice Kennedy in 1958.
His son-in-law is former California governor Arnold Schwarzenegger.
Mr Shriver also ran President Lyndon Johnson's "War on Poverty" programme.
Peace Corps director Aaron Williams said the whole movement was "deeply saddened" by Mr Shriver's death.
The BBC reports Mr Shriver's death came less than 18 months after that of his wife, who died in August 2009, aged 88.