Superman didn’t leap fully formed out of a void; he was part of a long tradition of heroes with amazing abilities and incredible costumes. It’s possible to try tracing him back to mythological figures like Hercules or Zeus, but he’s got at least three closer ancestors who sum up the stew of pop-culture influences around the beginning of the 20th century: The Shadow, John Carter of Mars, and Zishe “Iron King” Breitbart.
I’m least familiar with Breitbart – he was a Polish sideshow strongman who’d appear in Roman armor, sandals and cape, bending iron into pretzels… and in 1923 toured the States as “the Jewish Superman.”
I know I’ve read somewhere about Siegel and Shuster, the Jewish kids who invented Superman, maybe seeing Breitbart live, but it was only a maybe. He was one of many carnival strongmen, though – at the time, this was a really popular public entertainment – and things like tights, capes and symbols-on-chests were part of the visual language of the circus.
Pulp magazines are really where superheroes have their roots – early comics were basically pulps-with-pictures.
The Shadow has slightly complicated origins – starting out as a narrator for a radio series promoting Detective Story Magazine in 1930, then quickly becoming a hero in his own right, starring in his own magazine and fighting “the weed of crime” with a swirling cloak or overcoat and the “hypnotic power to cloud men’s minds.” He became a global phenomenon – here’s a 1937 episode with The Shadow voiced by Orson Welles, and you can hear an Australian version of a 1938 episode here. His written exploits (“as told to Maxwell Grant,” really writer Walter B. Gibson) were published twice a month until 1949.
The Shadow a crimefighter with an alternate identity of a man-about-town and a network of agents and helpers, a little like Doc Savage’s team of specialists. One of the key figures would be Margo Lane, a socialite who’s sometimes trying to discover the truth of The Shadow’s secret identity… not unlike Clark Kent’s early relationship with Lois Lane.
The Shadow is usually used to demonstrate the relationship of crime pulps with another comic-book hero, Batman. Both are dark figures with immense resources who seem, more often than not, to be prowling around the city at night and being generally spooky.
The idea of an alien with superhuman powers isolated on a distant world… with the ability to leap over tall buildings in a single bound… comes from even further back in time.
In 1911, Edgar Rice Burroughs, the same fellow who created Tarzan, started publishing a series of stories about John Carter, a Confederate captain miraculously transported to Mars, where the lower gravity gave him immense strength.
Like Superman in his first outings, Carter didn’t fly so much as jump really far. The plots are a lot more along the lines of colonial fantasies, with barbaric kingdoms easily tamed by Carter’s advanced ethics (?!) and two-fisted fighting style.
Unlike The Shadow or Iron King, Carter's actually described in most of his early adventure as, uh, not wearing a cloak, or cape, or overcoat, or, um, anything, really. Other than a harness.
The books were enormously influential – so much so, that the 2012 movie got some flak for being derivative… of all the fictions that the original novels inspired, from Flash Gordon to Dune to Star Wars (desert planets, alien princesses, hovering barges… even the names “sith” and “banth” are in Burroughs), and, yeah, Superman.
For further reading, I’d recommend Jess Nevins’ Encyclopedia of Pulp Heroes (currently online but hopefully in print soon), as well as, hey!, Edgar Rice Burroughs’ John Carter books, which are on Gutenberg (start with A Princess of Mars), and The Shadow radio plays, a healthy number of which are on archive.org.
Grant Morrison’s less rigorous (brilliantly rambling?) Supergods occasionally gets into the good stuff, too.