Along with the existence of his Earth-Two counterpart, Superman's Earth-One history was retroactively erased from continuity, after the conclusion of 1985-86 miniseries Crisis on Infinite Earths. The Post-Crisis Earth would be an entirely new continuity, but some aspects of the Earth-One version remained intact. However, Clark's career as Superboy, Supergirl, and Superman's tenure with the Legion of Superheroes were removed entirely from the new timeline. Writer John Byrne acknowledged that he intended to reintroduce several modified Silver Age aspects such as Superboy to the comics, but he was fired after two years due to "creative differences" with DC.