Furthermore, McGovern was partly responsible for the political primary system as we know it today. In 1969 the Democratic Party's McGovern-Fraser Commission vastly subdued the power of political bosses, making it easier for candidates to ride an ideology's popular support into a nomination; a tactic McGovern used when he left the commission in 1971 to run.
ABC News political analyst Matthew Dowd points out the election paved the way for Democratic leaders decades later.
"You can lose, but still basically carry the day," Dowd said on This Week today. "Without George McGovern we would have never had Jimmy Carter and we would have never had Bill Clinton."
Indeed, as Yale law school students Bill Clinton and Hillary Rodham both served as staffers on McGovern's Texas campaign. President Bill Clinton would go on to attend the dedication of the McGovern library in 2006.
In a written statement, Secretary Clinton said, "The world has lost a tireless advocate for human rights and dignity."
"Of all his passions, he was most committed to feeding the hungry, at home and around the world," she said. "The programs he created helped feed millions of people, including food stamps in the 1960s and the international school feeding program in the 90's, both of which he co-sponsored with Sen. Bob Dole."
A winner of the World Food Prize with the former Republican presidential candidate, McGovern served as the U.S. ambassador to the United Nations Agencies for Food and Agriculture from 1998-2001. He would also form the George McGovern-Robert Dole International Food for Education and Nutrition Program in 2000 to provide meals to children in the United States and around the world.
McGovern remained an active voice in public affairs until his final days, authoring books and continuing his anti-war message to Iraq and Afghanistan. He particularly assailed the rightward shift in the Republican Party and what he believed was a reluctance in progressives to speak up, for fear of seeming weak.
"For people who have never been near a battlefield […] to accuse critics of being soft on national security and soft on communism and soft on terrorism, I think is preposterous," he said in 2006.
Evoking former President Dwight D. Eisenhower's cautionary words on the power of the military-industrial complex, he warned of the dangers of unrestrained jingoism.
"Now a five-star general can say that without accused of being soft […] but I suppose a liberal Democrat – which I am – is not allowed to say that."
Today President Obama called him a "statesman of great conscience and conviction."
"When the people of South Dakota sent him to Washington, this hero of war became a champion for peace," he wrote.
The Associated Press and ABC's Huma Khan contributed to this report.