Batman and Robin (1949 movie serial)
This second serial moves a step closer to the formula we know and love with the introduction of a costumed villain called The Wizard replacing the World War II era Japanese saboteur of the first.
As far as I know The Wizard has never appeared in any other media.
Also featured is the character of photographer Vicki Vale, who wouldn't be seen onscreen again until the 1989 movie. I wonder why she was never seen in the 1966 TV series. A potential love interest for Bruce who was also trying to ferret out Batman's identity might have provided some nice comic moments, not to mention some competition for Catwoman.