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.