During World War II, he spent five years in the Navy and served in the Pacific.
When Shriver fell in love with his boss' daughter, he became a close and valued member of the famously clannish Kennedy family.
"Our brother-in-law became our brother," Sen. Edward M. Kennedy said in 2005. "We love him in our family."
Another of Shriver's brothers-in-law, John Kennedy — then a Democratic senator from Massachusetts — turned to Shriver in 1960 for help with his quest for the presidency. As manager of the civil rights arm of the campaign, Shriver engineered a feat that some say tipped the close election in Kennedy's favor.
When a young African American minister, the Rev. Martin Luther King Jr., was jailed in Alabama for civil disobedience, Shriver persuaded Kennedy to reach out to King and his wife, Coretta. The call was credited with helping to cement the crucial black vote for Kennedy.
The day after his inauguration, Kennedy asked Shriver to help him develop a program for young Americans to serve overseas. "Make it big," the president counseled. "Be fast, and be bold."
It was Shriver's idea to send Americans to the farthest reaches of the globe, bringing with them education, technology and a sense of fellowship that Shriver believed could break down barriers and win grass-roots respect for the U.S. He promised low pay, primitive conditions — and the reward of translating ideals into action.
His challenge was: "Be somebody. Join the Peace Corps." Of recruits, he required just three qualities: courage, commitment and conviction.
Lewis Butler, a California lawyer, said Shriver called him in 1961 and asked him to head the program in Malaysia. The concept was vague, but Shriver was utterly determined, Butler said. He recalled being unsure where Malaysia was.
"The first thing I did was run out and get a map so we could start the Peace Corps," he remembered. "I said, 'What are we supposed to do?' And he said, 'I don't know.' "
In 1962, when the program was already running in high gear, Shriver visited the volunteers in Malaysia and asked a nurse running a leprosy clinic if he could help. Soon Shriver was passing out bandages and medication to lepers, Butler said, and speaking to them as if they were heads of state.
"He was not just the head of the Peace Corps or its boss," Butler said. "He was the personification of its ideals."
Peace Corps volunteers arrived in five countries in 1961. In just under six years, Shriver developed programs in 55 countries with more than 14,500 volunteers. Since its inception, the Peace Corps has sent 200,000 volunteers to 139 countries. Today, more than 8,500 volunteers are serving in 77 countries.
After President Kennedy was assassinated in 1963, President Johnson asked Shriver to tackle the problem of poverty in the United States. At a 1964 news conference announcing his appointment as director of the Office of Economic Opportunity, a reporter demanded: "Mr. Shriver, do you really believe that poverty can be wiped out?"
Without hesitation, he replied, "Yes. I do."
In the next four years, Shriver unleashed a flurry of new programs. Using the Peace Corps as his model, Shriver crafted VISTA, a volunteer service corps aimed at U.S. cities. The acronym stood for Volunteers in Service to America. Head Start was designed to prepare underprivileged preschoolers for elementary school, just as private day care and nursery schools served more affluent children.
Community Action provided low-income housing. Foster Grandparents matched elderly volunteers with young children. Legal Services guaranteed lawyers to poor people. Indian and Migrant Opportunities brought training to Native Americans. Neighborhood Health Services targeted community medical needs.
Each of those programs remains in place today.