I just read The Scarlet Pimpernel and it's pretty much Batman set during the French Revolution. How far does the "hero with a secret identity trope" go back?
Wikipedia puts The Scarlet Pimpernel as the first in 1903, but the idea of a secret identity probably goes back further, right?
I have always heard it was The Scarlet Pimpernel too. Some people have thought it was Zorro, but he dates from 1919, considerably after 1903.
I think Pimpernel is the first story to feature the trope of wimp by day, masked superhero in secret. But there are some stories with similar elements. Like Shakespeare's Henry V, featuring a hard-partying, wealthy guy (Prince Hal of Henry IV) who is now trying to become a great king and warrior. He disguises himself as an ordinary man to walk among his troops and find out what they think. Not the same, but a few similar elements. Robin Hood, with his disguises and aristocratic background, may have similarities. Secret, masked freedom fighter for the common man, but really am aristocrat.