Superman of the Übermensch; they never acknowledged as much. Since 1938, Superman stories have been regularly published in periodical comic books published by DC Comics. The first and oldest of these is "Action Comics", which began in April 1938. "Action Comics" was initially an anthology magazine, but it eventually became dedicated to Superman stories. The second oldest periodical is "Superman", which began in June 1939. "Action Comics" and "Superman" have been published without interruption (ignoring changes to the title and numbering scheme). A number of other shorter-lived Superman periodicals have been published over the years. Superman is part of the DC
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.