Jim Jeffords ’56, a former three-term United States Senator from Vermont, died Monday morning at the Knollwood Military Retirement Residence in Washington, DC. He was 80.

Jeffords was most famous for leaving the Republican Party and becoming an Independent in 2001.

“”In order to best represent my state of Vermont, my conscience, and principles I have stood for my whole life, I will leave the Republican Party and become an Independent,” Jeffords said in his 2001 statement explaining the decision. “I have changed my party label, but I have not changed my beliefs. Indeed my decision is about affirming the principles that have shaped my career.”

At the time, he told reporters that he could not support a party that he thought had become too conservative and favored tax breaks for the wealthy over other domestic issues such as education.

His decision to caucus with the Democrats drew harsh criticism from his former party colleagues because the move single-handedly stripped the GOP of its Senate majority. Then-GOP Leader of the Senate Trent Lott of Mississippi characterized Jeffords’ switch as “the impetuous decision of one man to undermine our democracy.”

The announcement also catapulted Jeffords to national prominence. That week he appeared on the covers of Newsweek and TIME. He also received several death threats, requiring him to receive temporary Capitol Hill police protection. In the 2002 and 2004 electoral seasons, his celebrity served the Democrats well as a star fundraiser, raising millions of dollars for the party he refused to join out of respect for his family’s historic support for the Republican Party.

After his death, his spokesman of 15 years, Erik Smulson, said he had never been prouder of his time with the senator than in 2001 when Jeffords had made the decision.

“How he handled himself, how he stood for his principles. He was a great statesman, a great Vermonter, but an even better person,” Smulson said.

But even before he renounced his party allegiance, Jeffords was considered one of the last remaining moderate Republicans. At the point of his departure from the GOP, no Republican Senator had a lower score from the American Conservative Union.

As a Congressman in 1981, he was the only Republican to vote against President Ronald Reagan’s bill to slash the top income tax rate from 70 percent to 50 percent. He took notable stands in favor of affirmative action, gun control and President Clinton’s proposed national healthcare plan, many of which were issues few other politicians were willing to tackle at the time.

“He followed his sense of right in all that he did, and was never afraid to seek compromise by reaching across the aisle for the good of our country,” said Vermont Governor Peter Shumlin in a press release following Jeffords’ death. President Barack Obama released a statement mourning his death, adding that his “fiercely independent spirit” made him a trustworthy figure in national politics.

Born in 1934, Jeffords was the son of Olin Jeffords, the Chief Justice of the Vermont Supreme Court and a member of one of the most prominent Republican families in the state. A member of Silliman College, Jeffords graduated from Yale in 1956 with a Bachelor of Science degree in engineering.

After graduation, he served for three years as a gunnery officer on the Navy destroyer ship McNair. As a first-year officer, he participated in the reopening of the Suez Canal in 1957. When his military service finished, he attended Harvard Law in 1962. After a rapid rise in state politics  — which culminated in his tenure as the state’s Attorney General from 1969 to 1973 — Jeffords began his career in Washington after winning the 1974 election for Vermont’s sole seat in the House of Representatives. He remained in the House until 1988 when he was elected to the US Senate.

Even after his defection from the Republican Party, his reelection in 2006 appeared likely. Still, he declared in 2005 that he would not run for a fourth Senate term, citing his wife’s cancer and his own growing health concerns. He was soon diagnosed with Alzheimer’s disease.

Jeffords is survived by his children Laura and Leonard and their families.