In 1836 the United States government received a strange and unprecedented gift—a half-million dollar bequest to establish a foundation in Washington “for the increase and diffusion of knowledge among men.” The Smithsonian Institution, as it would be called, eventually grew into the largest museum and research complex in the world. Yet the man behind what became “America’s attic,” James Smithson, has remained a shadowy figure for more than 150 years.

Drawing on unpublished diaries and letters from across Europe and the United States, historian Heather Ewing tells his compelling story in full. The illegitimate son of the Duke of Northumberland, Smithson was the youngest member of Britain’s Royal Society and a talented chemist admired by the greatest scientists of his age. At the same time, however, he was also a suspected spy, an inveterate gambler, and a radical revolutionary during the turbulent years of the Napoleonic Wars. But at the heart of Smithson’s story is his bequest—worth $9 million in today in today’s currency—which sparked an international lawsuit and a decade-long congressional battle, featuring a dizzying cast of historical figures, including John Quincy Adams, and Alexander Graham Bell, both of whom grappled with how—and even whether—to put Smithson’s endowment to use.

Fascinating and magisterial, Ewing’s biography presents a sweeping portrait of a remarkable man at the center of the English Enlightenment and the creation of America's greatest museum.