As Gunn explained in a virtual press conference on Tuesday (which Variety moderated), Salvation will play a central role in Gunn’s 2028 “Superman” sequel, “Man of Tomorrow.” But both concepts will be narrative threads that will run through the entire DCU, including DC Studios’ next HBO Max series, “Lanterns.” “That was always pretty instrumental in the overarching story that I’m telling in the DCU,” he said. “I had mapped out what I thought the general story was, and two important aspects to that were Checkmate and especially Salvation.” So what is Checkmate and how is it introduced into the DCU?...