Kane decided to enlist the help of a friend, a freelance writer named Bill Finger, to help develop the paper-thin idea he had. This translated to getting someone else to do the bulk of the work for him.
"Bob's original vision included no story of any kind," Marc explains. "He drew the first sketches, which Bill then completely overhauled, including pointing to 'bat' in the dictionary and suggesting Batman's cowl resemble [an actual bat]." Finger also wrote Batman's "murdered parents" origin story, as well as the first stories to feature Robin, Catwoman, The Penguin, The Riddler, The Scarecrow, Commissioner Gordon, Gotham City, the batmobile, Batman's secret identity, and the nickname "The Dark Knight." Essentially, Bill Finger gave life to Batman in every sense of the word other than magically transporting himself into one of the comics and impregnating Martha Wayne. To reiterate, he did all of that work based on one Bob Kane illustration, which looked like this:
Bill The Boy Wonder: The Secret Co-Creator Of Batman
The best thing you can say about that design is, "At least there's no nipples."