He was an outspoken critic of one war, but a hero in another. He was a leading Democrat who came from Republican roots. He was a politician who cared more about being on the right side of an issue than on the popular side.

George Stanley McGovern -- a staunch liberal who served South Dakota in the U.S. Senate and House for more than two decades and who ran unsuccessfully as the Democratic Party nominee for president in 1972 -- died Sunday at the age of 90, his family said.

"Our wonderful father, George McGovern, passed away peacefully at the Dougherty Hospice House in Sioux Falls, SD, surrounded by our family and life-long friends," his family said in a statement.

"We are blessed to know that our father lived a long, successful and productive life advocating for the hungry, being a progressive voice for millions and fighting for peace."

President Barack Obama praised McGovern as someone who showed a lifelong love of country.

"When the people of South Dakota sent him to Washington, this hero of war became a champion for peace," the president said in a written statement. "And after his career in Congress, he became a leading voice in the fight against hunger. George was a statesman of great conscience and conviction."

Others remembered him for the changes he brought to politics.

"I think he'll be remembered, obviously, for his stance on the war in Vietnam," said Bill Richardson, the former governor of New Mexico, "but also for his contributions on agriculture, on hunger.

"And then the Democratic Party. He transformed the party, the primary system, getting minorities involved. He was a gigantic figure and a classy, good, good guy."

Funeral services are scheduled to take place in Sioux Falls on Friday, one day after a public viewing in the same city.

Bill and Hillary Clinton said they first met McGovern while campaigning for him in 1972. The former president and current secretary of state said McGovern never stopped speaking out for the causes he believed in.

"We must continue to draw inspiration from his example and build the world he fought for," the Clintons said in a written statement. "The world has lost a tireless advocate for human rights and dignity."

The son of a Methodist minister who was a Republican, McGovern was born in Avon, South Dakota, on July 19, 1922. Six years later, his family moved an hour north to Mitchell, where McGovern graduated from Mitchell High School in 1940.

His debating skills won him a scholarship to Dakota Wesleyan University in Mitchell, where he met fellow student Eleanor Stegeberg. Three years later, they married. All five of their children were born in Mitchell.

McGovern's political skills came to the fore in college, where he was twice elected class president and won the state oratorical contest on the topic "My Brother's Keeper," which laid out his liberal beliefs.

In 1942, he enlisted in the U.S. Army Air Forces and went on to fly 35 combat missions as a B-24 bomber pilot in Europe. He was awarded the Distinguished Flying Cross.

After the war, he returned to college, graduating in 1946. McGovern attended Garrett Seminary for a year before entering Northwestern University in Chicago, where he got his master's and doctoral degrees in American history and government.

He returned to Dakota Wesleyan University in 1950 as a professor of history and political science, leaving in 1955 to help the South Dakota Democratic Party and launch his political career.

In 1956, he won a seat in Congress. He was re-elected two years later.

After losing a bid for the U.S. Senate in 1960, McGovern was named special assistant to the president and director of the Food for Peace Program by President John F. Kennedy.

Two years later, he was elected to the Senate. He was re-elected in 1968 and 1974. He served on Senate committees on agriculture, nutrition, forestry and foreign relations, and the Joint Economic Committee. He also served three years on the Commission on Party Structure and Delegate Selection, which changed the way states picked their delegates, before leaving it in 1971 to run for president.

In 1972, McGovern was selected as the Democratic Party nominee for president on a platform that included ending the war in Vietnam at a time when the country was torn over U.S. involvement there.

"Let us resolve that never again will we send the precious young blood of this country to die trying to prop up a corrupt military dictatorship abroad," he said, to applause, at the Democratic convention in Miami Beach, Florida.

He called the unemployment of more than 5 million Americans "the most false and wasteful economics of all" and said his highest domestic priority would be "to ensure that every American able to work has a job to do." He called for an end to a system of economic controls "in which labor is depressed but prices and corporate profits run sky high," and he called for national health insurance and "a fair and just tax system."

But the campaign started out poorly. He selected as running mate Sen. Thomas Eagleton of Missouri, after a background check that did not turn up the fact that Eagleton had been treated for mental illness, which was revealed soon after. Eagleton withdrew and McGovern then tapped Sargent Shriver, a brother-in-law of John F. Kennedy and U.S. ambassador to France.