Frank Miller's classic Batman story The Dark Knight Returns, which features a climactic battle between the Caped Crusader and Superman, has seen a massive surge in sales following an announcement at San Diego Comic Con International that it would be a key text in defining the relationship between the characters in the forthcoming Man of Steel sequel, tentatively titled Batman vs. Superman. Variety reports that digital sales of the graphic novel are up 161% in July as compared to June, a number confirmed by the book's publisher, DC Comics. The Dark Knight Returns set a new record for sales of a regular-priced DC Comics ebook. The publisher has been aggressively courting the ebook market for graphic novels since June of 2012, when the first New 52 ebooks deployed in real time to Barnes & Noble's Nook. Shortly thereafter, Amazon's Kindle Fire and other devices were added. At Comic Con, Zack Snyder and actor Henry Lennix took the stage at the end of Warner Bros.' panel and announced the film, reading a brief passage from The Dark Knight Returns and then projecting a Batman/Superman logo on the walls of Hall H. At the Superman 75th Anniversary Panel later that day, DC Co-Publisher Jim Lee extolled the book's virtues as well. "I would also recommend The Dark Knight Returns by Frank Miller," Lee told the audience. "When I was in college, that's what inspired me to become a comic book professional in that it really took what I thought were professional stories and brought a whole new level of sophistication to them. He really represented Batman and Superman as almost these elemental forces that were representing all these different things--things that were very relevant in the '80s. In a way, Superman had lost his way a bit and was working for the Reagan Administration and--I don't want to spoil it--basically Superman and Batman fight in the end and I always thought Superman got robbed a little bit and it would be great to see a rematch between the two of them." "I don't know--maybe on screen?" He added, prompting screenwriter David S. Goyer to admit that, yes, the two would face off in the new film.