Hans Zimmer and James Newton Howard
Two guys took on the soundtrack to The Dark Knight, which actually owes a lot to the score for its predecessor, Batman Begins. Luckily, the same guys were attached to both projects, which makes straightening it all out a LOT easier.
Zimmer began life in Germany, but moved to London at an early age. He held a deep affection for synthesizers, and actually played the keyboards for a New Wave band called The Buggles, among others. (Trivial tidbit: you can see him in the Buggles' "Video Killed the Radio Star", which was the first music video ever played on MTV.) The need for a steady paycheck led him to composing jingles for commercials, and from there to film work. His big break took place in 1988, when he composed the score to the movie Rain Man. By the time Christopher Nolan pegged him for the Batman movies, he had twenty years of composition behind him: four or five a year. (Jeez, does he even take bathroom breaks?)
Howard was a little older, but he also had a background in rock and roll, having performed on tour with Elton John and Crosby, Stills and Nash, among others. He joined the composer party in 1990, with the Julia Roberts movie Pretty Woman. It became a big hit (though we're still trying to figure out why), and with it, Howard was off to the races. Like Zimmer, he did multiple films a year—every year—until Nolan pegged them to make Batman sound cool while brooding on rooftops.
The Dark Knight takes a lot of cues from Batman Begins. Including Batman's main theme and the quieter movements used for Rachel and Alfred. It worked really well. Zimmer was going to compose the Begins score solo, but wanted Howard along because he thought that two guys could really capture the split between Bruce Wayne and his broody, swoopy alter-ego.
They had a hard time getting there. Batman—and indeed superheroes of all stripes—were still in the thrall of Danny Elfman, who composed the score for Tim Burton's 1989 version of the Caped Crusader. (Like these guys, Elfman had a background in pop music, having fronted the band Oingo Boingo for many years. Apparently, rock stars compose film scores when they retire.) The Danster was working on Sam Raimi's Spider-Man pictures while Zimmer and Howard were trying to reinvent Gotham, and it took them a few tries to really escape from his dark carnival style tunes. They did it by going industrial, focusing on hard, clangy noises and cutting ties with Elfman's more whimsical approach.
For The Dark Knight, they doubled down on the clang, or at least Zimmer did. Howard got to handle Two-Face's theme, which he did with a straight-up orchestral piece—something noble and sad to show us how a seriously good guy can go so, so bad.
But the real juice belonged to the Joker, who Zimmer claims deserved a theme that everyone would hate in the best possible way. He almost scrapped it after Heath Ledger died, but we're weirdly glad he didn't. It plays like an atonal hurricane, all jagged bits and swirling chaos that make the eardrums bleed. Amnesty International probably has a file on what he does to stringed instruments here: word has it he actually had a cello played with a razor blade to make some of the sounds we hear.
He cites more of those death-metal industrial types like Kraftwerk for inspiration, but we've also spotted some threads of Bernard Herrman, a legendary composer who came up with the score for Psycho (among many others). That movie also revolves around a murderous psychopath, and like the Joker's theme in The Dark Knight, it does a lot of really awful things to the strings section. (Check out the main theme to Psycho and the infamous shower scene if you don't believe us.) Ironically, Danny Elfman also cites Herrman as one of his biggest musical influences, which should tell you how much Big Bernie means to musical scores in general.
In any case, it's hard to argue with the results. We get scared just listening to the Joker's theme, and the big-boom anarchy it represents fits in perfectly with the character it follows around. That's the centerpiece to a score that centers heavily on personality rather than action, which says a lot about why we're talking about this movie as legitimate art instead of just another take on Let's Beat Up the Bad Guys.