Former Delaware Gov. Mike Castle, a Republican moderate who championed creating the popular 50 State Quarters Program of commemorative coins while he served in Congress, has died. He was 86.

The Delaware Republican Party announced that Castle died Thursday in Greenville but shared no other details.

Castle was among Delaware's most successful politicians, never losing a race until his stunning upset in a 2010 primary for the U.S. Senate seat that Democrat Joe Biden held before becoming vice president.

During his 18 years in Congress, Castle became a leader of centrist Republicans, earning a reputation as a fiscal conservative and social moderate not afraid to challenge the party line on issues ranging from government spending to environmental protection and abortion.

As Delaware's lone representative in the U.S. House from 1993 to 2011, he supported a pay-as-you-go policy for both spending and tax cuts. Castle played roles in improving child nutrition programs and establishing the No Child Left Behind education reform program. 

His signature issue in Congress was the commemorative quarters program that featured coins honoring each state, starting with Delaware. He was dubbed by coin collectors as "The Coinage Congressman."

The quarters boosted federal revenues as they were taken out of circulation. He also helped establish a similar program honoring U.S. presidents with dollar coins, beginning in 2007, and an "America the Beautiful" quarter program honoring national parks, monuments and nature areas starting in 2010.

"The Honorable Michael Castle embodied the best of public service — moderation, integrity, and a steadfast commitment to all Delawareans," Delaware GOP Chairman Gene Truono said in a statement Thursday.

Castle had been a state lawmaker and lieutenant governor before becoming governor in 1985. He served two terms as governor.

Delaware Gov. Matt Meyer ordered flags flown at half-staff for the next week in Castle's honor.

"During his time as governor, Mike Castle visited every single school in our state, including mine, where he spoke to my high school class with the same warmth, humility, and commitment to public service that defined his career," Meyer, a Democrat, said in a statement. "That moment, among others, demonstrated what a good man he was and how deeply he cared about Delaware's future.

Rep. Sarah McBride, who holds the seat in Congress that once belonged to Castle, called him "a man of decency who understood the importance of respect and collaboration in public service, always working for the common good of our state of neighbors."

Sen. Chris Coons, of Delaware, remembered campaigning against Castle in a statement: "As we campaigned against each other, I only liked him more. There was an editorial written about how civilized we were. I am prouder of that column than almost anything."

Former Sen. Tom Carper said Castle "embodied what public service is supposed to look like: thoughtful, principled, and always grounded in doing what was right — not just what was easy, or what was popular — but what was right."