While most viewers eventually came around to Ben Affleck's depiction of Bruce Wayne/Batman in Batman v Superman: Dawn of Justice and Zack Snyder's Justice League, the Oscar-winning filmmaker was initially taken aback by how much negative fan reaction there was to his initial casting. Following the polarizing release of Man of Steel in 2013, Affleck was cast as the Dark Knight ahead of the release of Batman v Superman. There was an immediate, protracted backlash, which didn't really die down until the first trailer for Batman v Superman was released, and people started to see Affleck in the role.
At the time of his casting, Affleck had just released Argo, for which he won Best Picture and Best Adapted Screenplay at the Academy Awards. He was riding high, and to many (including, seemingly, Affleck himself), the internet's rejection of the mere idea that he could play Batman was a bit baffling.
"I was hurt," Affleck told The Howard Stern Show. "I was less hurt than I would've been 10 years earlier. But I was hurt because I felt like 'Wait a minute, come on. What do I got to do to' you know what I mean? Like, I'm just you know, like, 'Jesus Christ'...I thought it was an interesting idea but you know what? I also realized at that point...it's gonna be, 'Now this turns into a petition.' Now they got this thing, everybody's going to do a petition. You're really – a hundred thousand [signatures], you signed a f*cking petition like, you have anything better to do with your day than sign petitions? But, ironically, the reason I did this is I wanted to do a movie for my kids, particularly my son, that they would see and be proud of."
Obviously, Batman v Superman and Justice League were controversial in their own right, so even after Affleck himself got generally positive reviews, his tenure in the role was plagued by negativity surrounding the films. The Batman, which Affleck was set to write, direct, and star in, fell apart as Affleck decided he was done with the role, and now, less than a decade after his initial casting, Affleck is doing a farewell curtain call in The Flash, which will feature both his Batman and Michael Keaton's from Tim Burton's 1989 Batman. The mechanics of it are unknown, but it appears that by the time The Flash is over, Keaton will be the sole canonical Batman in the new DC Films universe, appearing in Batgirl shortly thereafter.