Danielle Allen never imagined that a hunt a decade ago to track down every early copy of the Declaration of Independence would lead her to a lesser-known British aristocrat who stoked the revolutionary ambitions of Thomas Paine and America’s founders beginning in the 1760s.

In a new book , “Radical Duke: How One Aristocrat — and the American Revolution — Transformed Britain,” Allen reveals that Charles Lennox, the third Duke of Richmond, was a rarely cited but important champion of then-radical democratic ideals, like popular sovereignty, grassroots political movements, universal male suffrage, and parliamentary reform.

Allen, the James Bryant Conant University Professor and director of the Allen Lab for Democracy Renovation at Harvard Kennedy School, discusses the mysterious duke’s hidden hand advancing the cause of democracy in Britian and an emergent U.S. The interview has been edited for clarity and length.

Gazette: You came upon the duke and his story somewhat by accident. What happened?

Danielle Allen: It was definitely an accident.

I published a book about the Declaration of Independence a bit more than a decade ago. That book led to a research project to try to track down every copy of the declaration produced between 1776 and 1826. That yielded the incredibly surprising discovery of a ceremonial parchment of the declaration in a small archive in southern England.

The world thought there was one ceremonial parchment; it’s in the National Archives. Lo and behold, it turned out there were two.

It quickly emerged that it seemed to have made it to the archives from the papers of Charles Lennox, the third Duke of Richmond.

But there was still a big mystery: How on earth did he get this document?

He was known to be a supporter of the Americans. He was the first member of Parliament to recommend recognizing American independence. So, it was in the pursuit of solving that mystery that I started researching the duke of Richmond, and then, to my great astonishment, found evidence that he was the first political patron of Thomas Paine and that Thomas Paine, who had said he never published anything before “Common Sense” in America in January 1776, had, in fact, been a radical writer in England for almost 20 years and had worked closely with the duke.

So, there was suddenly this huge window into this world of radical politics that had completely disappeared from view for historians.

You describe the duke as one of three major figures who shaped modern British constitutionalism, along with Edmund Burke and King George III. What made Lennox so significant?

He was the most unusual and interesting reformer. He introduced a bill for universal manhood suffrage in 1780, and that bill was a part of his vision about what it would take to constrain the executive power of the monarch.

His theory of the case for how to protect the liberty of British subjects depended on a strong Parliament and a Parliament that was fully connected to the whole people. That was a pretty novel conception. He had some allies at developing it, but he had that picture in view by the early 1770s, and he stayed on the case for decades.

He was an aristocratic Whig, was part of their political world, but he was also allied with the city radicals because they were interested in universal manhood suffrage. The aristocrats mostly didn’t get there except for him.

He also had a foot in with the county reformers because he was the lord lieutenant for Sussex County. He did a lot of work for his county.

Landed property owners who weren’t part of the aristocracy had a third vision for reform. He was the only person who was really allied with all three camps, and that made it possible for him to embed reform politics in the center of British politics from 1780 onward. He really laid the foundation for reform.

While the duke had a personal beef with King George III, he wasn’t necessarily pushing for a break from the crown as the Americans were. What was his aim?

His basic commitment was to British liberty, the liberty of subjects in the monarchy of Britain, but those liberties meant freedom of the press, freedom of trial by jury, freedom to have Parliament make decisions and not the king. His greatest concern was that the king was concentrating power in himself, and he was absolutely committed to blocking that.

The king had essentially a big slush fund that he used to both help people buy their seats in Parliament and that he also used to give people sinecures and rewards so he could command loyalty from enough members of Parliament to control the voting patterns. That meant Parliament had ceased to function in the 1770s as an independent body and that’s what Richmond objected to.

Tell me about the book’s big revelations: that the duke and Thomas Paine had been collaborating and that the duke quietly bankrolled and recruited writers to submit provocative political essays, known as the Junius letters.

It’s a pretty big deal from a historical point of view of understanding the dynamics of radical politics at the time. Richmond, in the 1760s, was in and out of government. He was extremely frustrated with the direction of British politics. He was also frustrated with the direction of his aristocratic peers.

Out of that frustration, he started hiring writers to write anonymous pieces in the newspaper that aligned with his agenda, and that practice evolved into a series called the Junius letters.

They’re a bit like the Federalist Papers. They offer a theory of constitutionalism, but they also had this really intense critique of the king and his government. In fact, they caused the collapse of one of the king’s ministries. And so, that’s the astonishing thing — who was behind those papers and how they fit into a broader agenda of reform.

How were you able to establish that so conclusively?

I was able to identify writers that the duke had worked with and had independent evidence for each of his specific relationships.

And then, reading the Junius letters really carefully, minutely, it’s very clear that their agenda tracks the duke of Richmond’s agenda. The details in them track his knowledge base and pieces of knowledge that he specifically would have had access to, things about the royal court, things about the cabinet, stuff like that.

So, there’s all these kinds of circumstantial evidence that made it very clear that there was this network of people working together and that they appear to be working on these Junius letters.

There were two other pieces of evidence that came into play. The first was the duke and his library. The library still exists. It’s beautiful; it’s like Thomas Jefferson’s library. The library includes anonymous and pseudonymous political pamphlets from the era. Some of those have inscriptions dedicating them to the duke.

One of those was this pamphlet nobody has really ever known about called “The Juryman’s Touchstone,” which is directly about the Junius letters and the sedition trials that came out of them. It has a long, handwritten dedication to the duke. I looked at it for three years, and finally, I was like, “Is it possible that this handwriting is Thomas Paine’s handwriting?”

I checked, and it was Thomas Paine’s handwriting. That was the smoking gun, the final proof that Paine and the duke were working together, and working together specifically on the Junius letters and the agenda connected to the Junius letters.

Then, I reached out to the people editing a new edition of Thomas Paine’s works that’s come out this summer to seek confirmation of my handwriting identification, and they provided that.

But then they also said, “Oh, by the way, we have developed this computer-assisted author authentication methodology to identify the authors behind pseudonymous works from the period. Can we check ‘Juryman’s Touchstone’?” They checked it and identified Paine and also Benjamin Franklin as the main authors of the text.

The duke had also contributed a paragraph about the House of Lords. As it happens, those scholars had also been working to identify the Junius authors, and, completely independently from me, they had come up with the same set of authors. So that was the clincher.

What is it about the duke’s story that so resonated with you and your work on democracy reform?

The 1760s and the 1770s were this amazing period when there was this problem of concentration of executive power. People were trying to figure out how to protect freedom in that context. That’s directly analogous to our current moment.

Modern political parties were just coming into existence for the first time, so people were trying to figure out how to balance alliances with specific people versus ideological agreements. When those things are in tension, what do I do? I think the democracy reform ecosystem right now has a lot of that going on in it.

Also, there’s a question of how do you navigate the politics to actually bring change? The duke was an incredible navigator of politics, really inventive and creative in producing new alliances and coalitions. Learning from somebody who is navigating similar dynamics is really helpful and fascinating.