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Clark Kent of Earth-96 and Bruce Wayne of Earth-99. Both are alternate versions of well-known heroes, based in part on how they were depicted in Kingdom Come, both older than they are normally portrayed, and both portrayed by actors who are famously connected to the characters. They've also both suffered terrible losses, but they handle those losses very differently; Clark managed to live with what he'd lost and go on living, even becoming editor-in-chief of the Daily Planet, but Bruce became a broken, insane old man haunting Wayne Manor with only Luke for company. Clark remained the beloved, kind-hearted hero he was, while Bruce descended into a bloodthirsty Knight Templar who grew to be feared and despised by the people he once protected. Clark embraces the mission to save the multiverse, rising to greater heights of heroism, whereas Bruce writes off not only his Earth, but every Earth as not worth saving, and dies in despair after one last act of villainy.
Kevin Conroy discussed with Entertainment Weekly how the "Crisis" role took him by surprise, stating how the experience of playing Batman for the first time in live-action "threw him" at first. "I never approached this character from that physicalized aspect. I always just inhabited him with my voice," Conroy said. "When you do that in a recording studio, it's a very intimate experience and you're sort of living in your own imagination. You do it with your eyes closed and you're in this other world, and you have Mark Hamill feeding you [need], and the other actors (because we always recorded together in the booths.)" "To actually be on the set, in the physical world, and to be walking as the character and inhabiting the character in three dimensions, it was a real transition for me," he added. "It did take a while to get used to, I have to admit. I was surprised because I know the character so well."
Executive producer Marc Guggenheim spoke of Kevin Conroy, "He is stupendous, He is Bruce Wayne. [It's] just a lot of fun to see this actor who we all mainly know from voice work being on camera. It was really exciting." Conroy's appearance in "Crisis" is the result of a dream. "One of the things that was always on my bucket list is that I wanted to see old Bruce Wayne," says Guggenheim. "We talked about a variety of different casting possibilities, but [Legends of Tomorrow showrunner] Keto Shimizu, who is a huge animated Batman fan, pointed out that Kevin is the right age. We reached out to Kevin and he couldn't have been more lovely and more game for it."
Sara tells Harbinger that she promised her crew no more crossovers, a breaking the fourth wall joke referring to how the Legends weren't part of the Elseworlds crossover.
Earth-99 is a reference to when Batman Beyond came out in 1999. Kevin Conroy played an older Bruce Wayne (actually much older than this one), who took a new young man under his wing to make sure that there would always be the new Batman of the future.
The Earth-99 Bruce Wayne has mementos/trophies of a bloody Joker card, The Riddler's cane, Mr. Freeze's jar that contained the ice sculpture of his wife Nora Fries, and possibly a plant under glass that may signify Poison Ivy and the glasses of that Earth's Clark Kent.