What WWII vehicle is the direct ancestor of the civilian Jeep?

The Willys MB is the World War II vehicle generally recognized as the direct ancestor of the civilian Jeep.

Willys-Overland produced the MB from 1941 to 1945 for the U.S. military. It was a compact four-wheel-drive utility vehicle powered by the 134-cubic-inch “Go Devil” inline-four engine. Ford also built a nearly identical version called the GPW, while American Bantam developed an earlier prototype, so the Jeep’s origins involved several companies.

After the war, Willys adapted the military design into the CJ, meaning “Civilian Jeep.” The CJ line began in 1945 and established the mechanical and visual relationship that eventually led to the modern Wrangler. The Ford GPW is therefore an important wartime counterpart, but Willys MB is the conventional single answer to this question.