Superman is widely considered (wrongly or rightly) the first superhero, if that's true who would be considered the second?
It depends on your definition of 'superhero'. There are older pulp heroes like Shadow or the Phantom, even Doctor Occult. But I guess Superman set the standard for the modern interpretation of the superhero.
As for the second? If Supes is the first, chronologically Zatara would be the second.
Wouldn't the first technically be Hercules from Greek Mythology?
Gilgamesh predates him as the first hero archetype
Hanuman was most likely the first Flying brick, Ghatotkaca (javanese) would be the first human-looking flying brick
without wings of course
He's the first one with a red cape
Doc Savage,The Shadow, the Phantom, Gilgamesh, Titan, Popeye, Mandrake the Magician, John Carter of Mars etc all came before Superman
You also have heroes in western folklore and mythology like Robin Hood, Hercules etc
Superman is the first superhero in terms of the first to go mainstream, and who set the blueprint for the modern day superhero. It's like with Hulk Hogan, he wasn't the first pro wrestler, but he was the first to go mainstream, and popularize the sports entertainer.
First comic book superhero (with powers) :Superman
First Superhero published: Springheeled Jack
Now to answer your question: Zatara would be second