When Superman blasted onto the scene in 1938’s Action Comics #1 (by Jerry Siegel and Joe Shuster), the world of comics was forever altered. Though their popularity would prove to vary over the decades, Superman’s emergence ultimately ushered in the age of superhero comics, an epoch that remains alive and well to this day. It’s no wonder, then, that imitators soon followed. Almost immediately, DC’s competitors were scrambling for the silver medal; they may not have been able to invent Superman, but they could copy him. The first to succeed in this was Fox Comics, who—as early as May 1939—debuted Wonderman in Wonder Comics #1 (by Will Eisner and Rick L. Philips).
Source：https://www.cbr.com/how-dc-briefly-lost-the-rights-to-superman-in-the-40s/
