Kryptonite is the name of a story arc written by Darwyn Cooke and Tim Sale that appeared in Superman Confidential, a monthly series that was published from January 2007 and then later cancelled in April 2008 that told stories set in the character's early years of his career. This arc, the first story from that title, tells the story of Superman's first encounter with kryptonite. Artist Tim Sale described the story's theme as "...Superman learning about vulnerability, and one of the ways that he had to learn it, and ultimately the most personal way, was through his relationship with Lois". With Superman: Secret Origin, it has been assumed this story arc is not in continuity anymore as of 2010. Source: Wikipedia (en)