Screenwriter: Jonathan Nolan and Christopher Nolan
Christopher Nolan and his little brother Jonathan are no strangers to screenwriting. They go all the way back to Christopher's first major motion picture, Memento, which he based on one of Jonathan's unpublished short stories. (Okay, they go back much further than that, but we don't want to get into that one time Chris tricked John into drinking pee when he was eight.)
The brothers served as active writing partners on four more movies since then: The Prestige, The Dark Knight, The Dark Knight Rises and Interstellar. The two have their own projects as well, Christopher directing those films (and a couple more) while Jonathan serving as the creator of the CBS show Person of Interest, but clearly their partnership has gone places.
Why Are They So Awesome? It's in the Blood
Naturally, their status as siblings gives them a leg up on other writing partners, for a number of reasons. Egos can clash in Hollywood, and the pecking order gets pretty brutal when it comes to writing a decent screenplay. (The Writer's Guild of America—the screenwriters' union—has very clear rules about who can take credit for what and when in order to avoid any unpleasant hissy fits.)
Not only can they get around that because of their sibling bond, but they can do so while still retaining the critical eye necessary to tell the other writer that his ideas need fixing. Sure, to the rest of Tinseltown, you're the biggest, baddest filmmaker in the world, but to your brother, you'll always be the one who went crying to mom every time you got a boo-boo. That gave them both the freedom to say "that stinks and you can do better" to each other without worrying about whether they'll still have a job.
Doing their Bat-Homework
To that brotherly bonding, they added some natural proclivities that make them ideal to tell this kind of story. For starters, they delved deep into Batman's comic book history to pen their tale, taking cues from screenwriter David S. Goyer who wrote the early treatments of the script. (Goyer gets a "story by" credit here, but no screenwriting credit.)
Specific comic-book storylines include The Long Halloween, which involved the early rise of Batman's villains; the original Batman #1 way back in 1940, which first introduced the Joker; and The Killing Joke, a graphic novel where the Joker shoots Commissioner Gordon's daughter in the spine and kidnaps him an effort to drive him insane. So yeah, they definitely played in the dark end of the comic-book street, which helped connect the movie's despairing tone with the fact that its hero runs around in a cape and a mask.
Beyond that, they had already shown an interest in psychologically damaged characters and crime stories, something that any Bat-writer worth his utility belt needs. (We'll go a little deeper into that over in the "Director" section.)
There's one other important detail worth mentioning here. Both the Nolan boys spent a great deal of time in Chicago growing up, and Jonathan still considers himself an adopted son of the Second City. That shows up in the little details of the film, not just in the gangster angle (which Chicago was quite famous for), but in tons of details that Chicagoans can probably spot. ("Gee, that river looks awfully familiar...") Again, we'll get into that a little more over in the "Setting" section, but clearly, the Nolan boys wanted to stick close to home.
All in all, it makes for a heck of a one-two punch: two brothers whose talents complement each other perfectly, and who combined to tell one of the greatest Batman stories ever told. In the space of a few short years, they've become some of the best-known and most critically respected filmmakers in the world. What's a little pee drinking compared to that?