Detroit— The Smithsonian Institution has been on a two-year hunt for a fabled oil painting of legendary Detroit business tycoon Berry Gordy Jr., founder of Motown Records. The portrait: Gordy dressed as Napoleon.

The painting, created by a Detroit artist, is just as it sounds. Gordy, the brilliant, autocratic founder of one of the most iconic music labels ever, is depicted in early-19th-century military garb of the French emperor who tried to conquer the world.

“Berry said, ‘Damn, I like that,’” the artist, DeVon Cunningham, recalled Gordy commenting when he first saw the portrait that had been commissioned by Gordy’s sister.

That was in 1969 at Gordy’s former Boston-Edison home in Detroit. And that was the last time Cunningham saw the portrait....