Superman: Whatever Happened to the Man of Tomorrow? reference to one of the nicknames of Superman as the "Man of Tomorrow", and was later again used in the title of another Superman . The comic book, "Action Comics" #1, published in April 1938 by "National Allied Publications" (later renamed DC Comics), marked the first publication of the character of Superman created by Jerry Siegel and Joe Shuster. The comic quickly became a success, and its editor soon realized that it was because of the popularity of the character. In an unprecedented move at the time, National Allied Publications introduced a second comic book, "Superman", exclusively featuring the popular
Superman Universe, which is a shared universe of superhero characters owned by DC Comics, and consequently he frequently appears in stories alongside the likes of Batman, Wonder Woman, and others. Superman has sold more comic books over his lifetime than any other American superhero character. Exact sales figures for the early decades of Superman comic books are hard to find because, like most publishers at the time, DC Comics concealed this data to deny competitors, but sales of "Action Comics" and "Superman" probably peaked in the mid-1940s and thereafter steadily declined as part of a general trend in comic book sales.