WASHINGTON – Former Indiana Sen. Richard Lugar, a foreign policy icon in the Senate who received the nation's highest civilian awards for his efforts to secure and destroy weapons of mass destruction after the collapse of the Soviet Union, died Sunday, according to his family.

The cause of death was complications of chronic inflammatory demyelinating polyneuropathy.

“The world weeps alongside Indiana after just learning we lost one of our best, ever," Indiana Gov. Eric Holcomb said. “He was an officer and gentleman, father and faith leader, a mayor and senator, a diplomat and legendary role model to millions."

Vice President Mike Pence, who called Lugar a friend and mentor, said Lugar leaves behind a legacy of public service that will inspire Hoosiers for generations.

Lugar, 87, was mayor of Indianapolis from 1968 to 1975 and served in the Senate from 1977 to 2013.

He was president of the nonprofit Lugar Center, which he launched in 2013 to continue work on many of his policy priorities – finding solutions to energy security, world nutrition, effective governance, controlling weapons of mass destruction and other issues.

Lugar is survived by his wife, Char, and his four sons, Mark, Bob, John and David. Their families were with him throughout his short illness, according to a statement.

Few senators in history served longer than Lugar or earned as much respect.

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"Dick Lugar's decency, his commitment to bipartisan problem solving, stand as a model of what public service ought to be," President Barack Obama said when awarding him the Presidential Medal of Freedom in 2013. Lugar received the Defense Department's highest civilian award in 2012.

The Russian Embassy in Washington recognized Lugar's accomplishments in a tweet Sunday that read, "R.I.P. Senator Richard Lugar."

Lugar had been a leading voice for decades on foreign policy, helping create a highly respected program to reduce the chance of nuclear annihilation. He also tried to mitigate hunger around the world and in schools, and warned about the national security consequences of fossil fuel dependence.

In 1990, he started the Lugar Series, a training ground for Republican women leaders that has inspired similar programs in other states.

"I know countless individuals who are in the leadership positions they are today, because of Senator Lugar," said Indiana Lt. Gov. Suzanne Crouch.

An ardent runner and physical fitness advocate, he initiated a series of health festivals in Indiana. In 1983, he founded a scholarship program for minority students.

Lugar, however, was known almost as much for his style as for his accomplishments.

Always courteous if somewhat stiff, he was considered one of a vanishing breed of statesmen who thought less about short-term political gain and more in putting in the hard work on hearings, investigations and diplomacy – including a willingness to work with those on the other side to get things done.

"Dick Lugar was not just the finest public servant I will ever know, he was the finest person," said former Gov. Mitch Daniels, a former top aide to Lugar. "He embodied all we can hope for in our leaders: brilliance of mind, purity of motive, stainless in character, tireless in the pursuit of duty."

Kevin Kellems, another former aide, called Lugar a one-of-a-kind hybrid of old school historian-politician, plus serious policy workhorse, plus international chess player.

"Above all, Dick Lugar was a kind and generous man who cared deeply about the future and welfare of children," Kellems said.

The Almanac of American Politics said Lugar's strength had been to follow "where his stubborn convictions and his considerable intellect led, regardless of political risk or reward."

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While Lugar enjoyed plenty of successes throughout his career – including many awards and Nobel Peace Prize nominations – his disappointments included an unsuccessful bid for the 1996 GOP nomination for president and being passed over as a running mate for George H.W. Bush in favor of Indiana colleague Dan Quayle in 1988.

When he sought a seventh term in 2012, Lugar was beaten in the primary by Tea Party candidate Richard Mourdock, who went on to lose to Democrat Joe Donnelly in the general election. At the time of his defeat, Lugar was the Senate's most senior Republican.

Donnelly, on Sunday, said he is "personally crushed" by the loss of Lugar, "a hero and a mentor to me."

Lugar always took the long view, saying once that there are times when you lead but are not always followed: "A gentle, thoughtful, persuasive, persistent but wise course of action is a winner."

A native of Indianapolis, he received numerous awards and distinctions, including at least 18 honorary college and university degrees.

He graduated in 1954 from Denison University, where he served as co-president of the student body with his future wife, Charlene Smeltzer. He also won a Rhodes Scholarship, the first Denison student to have done so.

At Oxford University, Lugar studied politics, economics and philosophy, receiving a master’s degree from Pembroke College. Even though he was the only American at Pembroke, he was elected president of its student body.

For three years, he was on active duty in the Navy, serving as personal intelligence briefer for Chief of Naval Operations Admiral Arleigh Burke.

In 1960, he returned to Indianapolis, and with younger brother Tom, purchased controlling interest in his father’s family’s 605-acre livestock and grain farm in southeast Marion County and his mother’s family’s Thomas L. Green and Co. Inc., manufacturers of food production machinery.

Lugar’s political career began in 1964 when he successfully ran for the Indianapolis Board of School Commissioners. As school board vice president, he was active in the desegregation of city schools.

In 1967, he was elected the first Republican mayor of Indianapolis in 20 years, upsetting incumbent John J. Barton by 9,000 votes. Four years later, he was re-elected with 60 percent of the vote.

In just his second year as mayor, in 1969, Lugar and other advocates successfully pressed the Indiana General Assembly to extend Indianapolis city limits to the Marion County line.

The impact was seismic: Called Uni-Gov, the initiative enlarged the city into the suburbs, streamlined many government services and boosted the power of the Indianapolis mayor, while creating a 29-member City-County Council.

Uni-Gov has been credited with revitalizing the city, setting the stage for major gains in infrastructure and the development of Indianapolis' sports institutions and arenas.

Lugar later recalled of Uni-Gov: "That was an experiment that said that a city can remain whole, that it can have a vital center as well as vital neighborhoods and suburbs, as opposed to being a hollowed-out shell as so many cities were and have become."

Lugar was elected president of the National League of Cities and vice president of the Advisory Commission on Intergovernmental Relations.

Lugar first ran for the U.S. Senate in 1974, losing to Democratic incumbent Birch Bayh’s 50.7 percent of the vote.

Despite a Democratic trend that year, Lugar ran 100,000 votes ahead of the rest of the Indiana Republican ticket.

In 1975, Lugar chose to not run for a third term as mayor and taught politics, ethics and local government as a visiting professor at Indiana Central University, which since became the University of Indianapolis.

He was elected to the Senate in 1976, defeating incumbent Democrat Vance Hartke with 59 percent of the vote and carrying 82 of Indiana’s 92 counties. Six years later, he was re-elected by 150,000 votes – the biggest victory margin of any Republican in the Midwest that year.

While he would become part of an increasingly small ideological middle in the Senate, he was viewed for years as a reliable conservative. In his first two years, Lugar co-led a successful effort to filibuster changes to labor laws sought by unions.

Although he was the leading sponsor of a 1980 bill to provide loan guarantees to Chrysler, a major Indiana employer, he did so only after gaining wage concessions from workers.

Throughout his 36 years, Lugar sat on the Senate Agriculture, Nutrition and Forestry Committee, where he looked out for Indiana farm interests, particularly in his championing of biofuels.

"He was a strong ally in promoting conservation and renewable energy," Iowa Sen. Chuck Grassley said Sunday.

But Lugar, who continued to manage his family's farm, also opposed many federal farm programs. He led the 1992 effort to close some USDA field offices and tried for years, with varying degrees of success, to eliminate certain crop subsidies.

A longtime advocate for hungry children, Lugar sometimes defied his party leadership or powerful constituencies to fight for anti-hunger programs. That began with his first days as an elected official on the Indianapolis school board and continued in Congress where he led efforts to stop a 1995 move to turn the federal school lunch program into a limited block grant.

“Senator Lugar’s dedication to nutrition programs that help Americans at risk of hunger will leave a legacy of service that define an era of compassionate care for the neediest amongst us," said Emily Weikert Bryant, executive director of Feeding Indiana’s Hungry.

Lugar's top interest was foreign policy, a bug that bit him when he served in the Navy as an intelligence briefer.

After Lugar became chairman of the Senate Foreign Relations Committee in 1984, he was credited with restoring the prominence of the panel, which had been torn apart by ideological differences and relatively weak chairmen. Lugar instigated a broad review of foreign policy and, according to Congressional Quarterly's Politics in America, became almost a shadow secretary of state.

Congressional correspondent John T. Shaw wrote in his 2012 book on Lugar that he was one of the most influential U.S. senators on foreign policy for more than a quarter century.

Lugar's ability to convince President Ronald Reagan that the 1986 election in the Philippines was fraudulent and Ferdinand Marcos should be persuaded to leave was viewed as one of the Reagan administration's top foreign policy achievements.

But Lugar handed Reagan one of his biggest defeats when he led the Senate in overriding Reagan's veto of a bill imposing economic sanctions on South Africa over apartheid.

"The American people felt very strongly that narrow sanctions on the leadership of South Africa might lead to freedom for Nelson Mandela and certainly put the United States on the right side of history," Lugar later said.

Lugar was the Senate point man for the George H.W. Bush administration during the first Persian Gulf War. But he was unable to get the administration to address his concerns about its handling of the 2003 invasion of Iraq and planning for its aftermath.

Lugar's greatest achievement was working with then-Sen. Sam Nunn, D-Ga., to create a program to secure or dismantle weapons of mass destruction in the former Soviet Union. The Nunn-Lugar Cooperative Threat Reduction Program, which began in 1992, passed without the support of the George H.W. Bush administration and with little initial enthusiasm from Congress. Its successes include deactivating 7,619 nuclear warheads once aimed at the United States, destroying 902 intercontinental ballistic missiles and 2,855 metric tons of chemical weapons agent, and building 38 biological threat-monitoring stations.

“Our nation has lost an extraordinary statesman who made the world a safer and better place," Nunn said Sunday. "I have lost a wonderful friend and trusted partner. "

The program was nominated for a Nobel Peace Prize multiple times since 2000, even while Lugar continued to travel regularly to oversee the program and work in Congress to expand it to other countries and to conventional weapons.

"He's one of the few senators who has both a landmark law under his name but has also spent 20 years making sure it's implemented well," Shaw previously said.

Lugar also devoted considerable attention to the global security consequences of oil dependence and climate change.

Although Lugar continued to vote with his party the majority of the time, he crossed party lines on issues that angered some conservatives, including advocating a path to citizenship for some children of illegal immigrants, approving a ban on assault weapons and voting for Obama's Supreme Court nominees.

After leaving the Senate, Lugar worked with Georgetown University's McCourt School of Public Policy to create a bipartisan Index that ranks how often members of Congress work across party lines.

"Dick Lugar personified the thoughtful bipartisanship so much missing in America today," Senate Minority Leader Chuck Schumer, D-N.Y., tweeted Sunday.

Senate Majority Leader Mitch McConnell, R-Ky., said Lugar combined the principled commitments of a patriot with the political instincts of a savvy legislator.

"He was a wise counselor and leading voice within the Republican conference and an inexhaustible bipartisan collaborator who earned the admiration of everyone across the political spectrum," McConnell said.

Indiana Sen. Todd Young, who got his start on Capitol Hill working for Lugar, said he doubts the nation "will ever see another Richard Lugar."

"But I pray that we do," Young said. "May God watch over him and his family.”

IndyStar contributed to this story.