"The sketch of the movie was Batman hates Superman because he doesn't have the perspective of a god," Snyder explained. "So when Superman comes to Metropolis, [Bruce Wayne] just sees the destruction — he doesn't see the ‘why’ of [his battle with General Zod]. He doesn't realize its global consequences. Thousands to save billions, right? And Superman hates Batman because he believes in the rule of law, and is like, 'Bro, like, judge, jury, and executioner? That's not cool!'”

But Snyder also understood that his two marquee superheroes couldn’t actually destroy each other, and needed to set aside their differences in the film's final act. “In the sketch, I'm like, 'So they fight, and there has to be another thing that draws them together in the end,’” Snyder said. “And then that's the thing that kills Superman, eventually."

The second half of the film's title, Dawn of Justice, presages the two Justice League movies, part of Warner Bros.' betting-the-company slate of interconnected films based on DC Comics titles. As they began assembling the narrative threads that would bind those movies together, Snyder and his creative team — including his wife and producing partner Deborah Snyder, producer Charles Roven, and DC Entertainment guru Geoff Johns — decided that the person who unites the Justice League should not be the all-powerful Superman.

"I really felt like Bruce should be the one that puts the Justice League together," said Snyder. "He feels like the samurai who would do that, who gathers the others."

And, finally, Snyder also had to consider how Batman v Superman would set up the two-part Justice League. "The catalyst, the need for the Justice League, has to rise from something," he said. These powerful superheroes, in other words, couldn’t just get together for a picnic. So, as Lex Luthor (Jesse Eisenberg) intones at the end of Batman v Superman, that "something" ended up being the death of Superman — a cosmic bell that cannot be unrung, and would signify that Earth was suddenly vulnerable.

"To me, [Superman's death] solved so many great problems," said Snyder.