The First 20th Century Masked Hero?

 Just in case you have no idea….

Wikipedia https://en.wikipedia.org/wiki/Emma_Orczy

Baroness Emma Magdolna Rozália Mária Jozefa Borbála “Emmuska” Orczy de Orci (/ˈɔːrtsiː/; 23 September 1865 – 12 November 1947) was a Hungarian-born British novelist and playwright. She is best known for her series of novels featuring the Scarlet Pimpernel, the alter ego of Sir Percy Blakeney, a wealthy English fop who turns into a quick-thinking escape artist in order to save ill-fated French royalty from “Madame Guillotine” during the French revolution, establishing the “hero with a secret identity” in popular culture

There could be an argument for earlier characters (Pirate Prince, etc) but the popularity of the secret identity and playboy fop was to be far reaching in pop culture.

One thing that Comic Bits (the publication) tries to do is make sure that these characters and creators are not forgotten. CB tends to focus on UK characters and creators and Orczy was living and working in London so qualifies.