In 1939, six episodes of a movie serial were shot and ready for distribution, but quickly swept under the rug when the plug was pulled.
"MYSTERY OF THE BAT-MAN!" was an early pitch, by Bob Kane and Bill Finger, to a little known poverty row studio in Hollywood, just as their now-iconic character was building momentum in the pages of Detective Comics (*this was years before Columbia Pictures released their much more well-known serial in 1943.)
In March, 2016, a box of one-of-a-kind 16mm prints, and artwork related to the project, turned up in a barn outside Beeville, Texas. Currently a costly restoration is underway to shine light on this earliest Batman media adaptation.