Alternative versions of Superman establish a new continuity for DC, affecting not only Superman, but all of the DC Comics characters. The versions of Superman from this time period are traditionally divided into three main periods. The first version of Superman began being published by DC Comics in 1938 appearing in "Action Comics" #1. To explain discrepancies in the aging of Superman across several decades, his earliest stories were retroactively portrayed as having taken place on an alternative world called Earth-Two. These stories take place from 1938 until the late 1950s, although the exact dividing line is unclear and some stories happened identically to
Adventure Comics adventure series. In issue #12 when the series was titled "New Adventure Comics", Joe Shuster and Jerry Siegel introduced the first version of the character Jor-L as a science fiction detective in the far future; the character would eventually become the alien father of Superman, although the first Superman story, in "Action Comics" #1, would not appear until more than a year after Jor-L's first appearance. The series' focus gradually shifted to superhero stories starting with the debut of the Sandman in issue #40. Other superheroes who appeared in the early days of "Adventure" included Hourman (from #48 to #83);