Once word got out that a new standalone Batman film was on the way, it naturally didn't take long before rumours began to spread about every aspect of the upcoming production. After it was finally confirmed that Ben Affleck would be directing and co-writing the film, official announcements soon began to flow. Ben Affleck himself shared a video of Deathstroke and it was later announced that Joe Manganiello would be stepping into the villains boots. While Deathstoke will make his first appearance in JUSTICE LEAGUE, he'll go on to serve as the main villain in the standalone Batman film, which Affleck recently announced will be titled THE BATMAN, at least for the time being.
As for why Ben Affleck wanted Deathstroke to face off against Batman, the actor chatted with Collider recently to reveal his thoughts behind the choice.
He’s a great villain because—I just had an instinctive feeling that he would match up with him well. You know, I’m a big admirer of that character as well, especially in the New 52 the way that they did Deathstroke, and I thought that it could work.
The New 52 incarnation of Deathstroke which Ben Affleck mentions had already been a top mercenary for quite some time when the series kicked off, much like Batman had already been active for a number of years in BATMAN V SUPERMAN: DAWN OF JUSTICE, so I'd imagine that Affleck was likely attracted to witnessing these two seasoned veterans going head-to-head. JUSTICE LEAGUE will hit theaters on November 17, 2017, but THE BATMAN doesn't have an official release date just yet.