This Wikipedia entry discusses the development of the 4CV. It was a clandestine wartime project that neither the Germans nor Louis Renault would have approved of, though it seems both got wind of it -- but didn't squelch it. I won't go into the revanchist government takeover of Renault and the death of Louis, but the entry does, and further mentions the strange episode where Ferdinand Porsche got dragged into the 4CV situation and might have paid for it in terms of jail time.
As for the 4CV itself, its engineering designers got caught up in the rear-engine fad of the 1930s that spilled over into the postwar years, so the 4CV had its motor placed in the rear. The car was about the same size as the pre-war Juvaquatre, and so was to that degree in line with previous Renault practice.
The slightly earlier in terms of design, if not market entry, Volkswagen Beetle had its engine at the rear, but it was air-cooled, whereas the 4CV motor was water-cooled. The Beetle had two doors, but the 4CV yielded to the strong French preference for four doors. Aesthetically, the Beetle had aerodynamic pretensions, while the 4CV featured cramped conventional styling on its small layout. The 4CV sold well by prewar French standards and the Beetle was a fabulous marketplace success.
Let's take a closer look at the 4CV's styling.