Sitting down with co-stars Henry Cavill and Amy Adams on The Graham Norton Show, the 43-year-old Oscar winner revealed that he originally didn't think he was right to play the iconic vigilante.
"Zack came to me and said, 'I want you to do this Batman [movie],' and I said, 'I don't think I'm really right for this,'" Affleck said, admitting that he couldn't see himself playing a "young guy who's avenging his parents' death and goes and puts on a cowl and fights super-villains."
That's when Snyder explained that this Batman is different than any other live-action portrayal of the Dark Knight.
"[Snyder] said, 'No, no, no! That's not it. He's completely broken down, he's older, he's falling apart and on the verge of moral bankruptcy! You're perfect for it!'" Affleck recounted, laughing.
In the gritty action epic, based in part on Frank Miller's 1986 graphic novel, The Dark Knight Returns, Batman has already been fighting crime for over two decades and has become bitter and jaded. It was this darker, more brooding take on the character that apparently attracted Affleck to the role.
"I really like what Henry had done and Amy had done in Man of Steel, and I really liked the version of the Batman they were doing," Affleck explained, adding that "the risk" of taking on such a beloved character "was very appealing."
While Batman v Superman debuted to huge returns, raking in over $166 million domestically in its first weekend, it hasn't fared as well with critics. However, Affleck is still set to reprise his role in the upcoming The Justice League Part One and Two, as well as a reported standalone Batman film that Affleck himself it set to direct.
Check out the Batman v Superman cast's full interview when The Graham Norton Show premieres Thursday, March 31 at 11/10c on BBC AMERICA.