The DC foreign policy community reacted with shock and sadness Monday to the unexpected death of Rich Williamson, a long time American diplomat and Republican foreign policy operative, who died Sunday due to complications from a cerebral hemorrhage at age 64.

Williamson most recently served as a top foreign policy advisor to Mitt Romney and helped shape the 2012 GOP nominee's policies on international affairs. But Williamson's resume also included stints as a diplomat, political candidate, academic, lawyer, human rights activist, and key figure in the foreign policy staffs of leading Republican politicians including Sen. John McCain. Williamson also worked on two presidential campaigns for Ronald Reagan and was a junior staffer in the Reagan White House.

Among his many titles, Williamson served as assistant secretary of state for international organization affairs under Reagan, as assistant to the president for intergovernmental affairs under George H.W. Bush, and was appointed by George W. Bush as ambassador to the U.N. for special political affairs and ambassador to the U.N. Commission on Human Rights. He was the Republican nominee for the U.S. Senate in Illinois in 1992 and authored 8 books as well as hundreds of articles.

At the time of his death, Williamson was a senior fellow at the Chicago Council on International Affairs, ran his own consulting firm called Salisbury Strategies, and served as vice-chairman of the International Republican Institute, an NGO focused on democracy and human rights promotion abroad.

Several former colleagues and friends noted in interviews Monday that Williamson's success across many fields and over many decades was in no small part due to his large and warm persona and his unshakable confidence in his convictions, which centered around putting human rights and the responsibility to protect those in peril at the fore of foreign policy considerations.

“The first thing you think about Rich was that they guy was an ardent believer in American exceptionalism. He was also a partisan Republican. He believed in the party,” said Robert O'Brien, a U.S representative to the U.N. General Assembly in George W. Bush's adminstration. “As tough as Rich was, he always did it with a smile, enjoyed the game, and respected his adversaries.”

Williamson's former boss, John McCain issued a statement expressing his grief as well. "I worked closely with Rich for decades We shared a belief in the vital importance of American leadership in the world and that our nation’s security is inextricably linked to our values of freedom and democracy. I always admired Rich’s intellect and judgment, and sought his counsel often."

Although he had long ties to McCain and other GOP leaders, Williamson was a relatively new face in the Romney orbit at the beginning of the 2012 campaign, but quickly became Romney's go to guy on all national security issues. “If Romney had won, he could have become his national security advisor, and he would have been one of the great national security advisors in American history,” O'Brien said.

In a statement on Monday, Romney said of his campaign aide “Time and again, Rich put aside the fruits of lucrative private practice to answer the call to serve our country. His was a consistent call to strengthen our alliances, to face down tyranny, and to share the promise of freedom around the globe. A man of conviction, courage and constancy. I will miss him and the nation will miss his dedicated service.”

Williamson's work as Special Envoy for Sudan during the George W. Bush administration is credited with helping to lay the groundwork for partition of Sudan and South Sudan obtaining nationhood in a much less violent way that it could have.

Eric Cohen, the co-founder of the non-profit Act for Sudan, said Monday, "We’ve lost a true hero for Sudan’s people." Cohen added, "Upon becoming U.S. Special Envoy to Sudan, Ambassador Williamson quickly understood the nature of the Sudan regime and that sticks, not carrots were needed to change the calculations of a government whose leaders had been indicted for genocide, war crimes and crimes against humanity. Ambassador Williamson worked tirelessly for the Sudanese people, seeing the Khartoum government for what it really is and saying so, even long after he was the Special Envoy."

Alex Wong, who worked closely with Williamson as foreign policy director on the Romney campaign, noted that Williamson was never shy about taking a tough stance but always stayed in the debate until the end and wanted to engage his adversaries as much as possible.

“Rich really was a diplomat in the mold of all great diplomats in that he knew that his job wasn't to elide differences between the U.S. and other nations but really to represent our principles and truly fight for them with clarity,” Wong said. “Even if he was delivering a message the other side didn't like, they really couldn't help like the guy delivering the message and that was a key to his success.”

Williamson leaves behind his wife, Jane, and four children. Funeral arrangements are still pending, but viewing is likely to be Friday afternoon, December 13, with services on Saturday, in Kenilworth, IL.

He often outlined his strategy for advancing America's foreign policy objectives by saying: “You have to be a realist to take steps day to day, but you have to be an idealist to know where you are going.”